U.S. patent application number 13/819226 was filed with the patent office on 2014-05-29 for motion control system of vehicle.
This patent application is currently assigned to Hitachi Automotive Systems, Ltd.. The applicant listed for this patent is Toshiya Oosawa, Shinjiro Saito, Junya Takahashi, Makoto Yamakado. Invention is credited to Toshiya Oosawa, Shinjiro Saito, Junya Takahashi, Makoto Yamakado.
Application Number | 20140145498 13/819226 |
Document ID | / |
Family ID | 45893122 |
Filed Date | 2014-05-29 |
United States Patent
Application |
20140145498 |
Kind Code |
A1 |
Yamakado; Makoto ; et
al. |
May 29, 2014 |
MOTION CONTROL SYSTEM OF VEHICLE
Abstract
Vehicular motion control system comprising controller that
independently controls driving force and/or braking force of each
of four wheels and a turning direction sensor that senses a turning
direction, and with an acceleration/deceleration command generator
that generates an acceleration/deceleration command based upon a
sensed steering angle and sensed vehicle speed and a driving
force/braking force distributor that determines the distribution of
driving force or driving torque and/or braking force or braking
torque of each wheel, and driving force/braking force distributor
determines based upon the acceleration/deceleration command and the
turning direction so that more driving force or more driving torque
and/or more braking force or more braking torque are/is distributed
to the inside front wheel in turning than the outside front wheel
in turning and more driving force or more driving torque and/or
more braking force or more braking torque are/is distributed to the
outside rear wheel.
Inventors: |
Yamakado; Makoto;
(Tsuchiura, JP) ; Takahashi; Junya; (Saitama,
JP) ; Saito; Shinjiro; (Kasumigaura, JP) ;
Oosawa; Toshiya; (Yokohama, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Yamakado; Makoto
Takahashi; Junya
Saito; Shinjiro
Oosawa; Toshiya |
Tsuchiura
Saitama
Kasumigaura
Yokohama |
|
JP
JP
JP
JP |
|
|
Assignee: |
Hitachi Automotive Systems,
Ltd.
|
Family ID: |
45893122 |
Appl. No.: |
13/819226 |
Filed: |
September 28, 2011 |
PCT Filed: |
September 28, 2011 |
PCT NO: |
PCT/JP2011/072295 |
371 Date: |
May 29, 2013 |
Current U.S.
Class: |
303/3 ; 303/140;
701/69 |
Current CPC
Class: |
Y02T 10/72 20130101;
B60W 30/02 20130101; Y02T 10/7258 20130101; B60W 10/184 20130101;
B60W 2720/403 20130101; B60W 30/045 20130101; B60T 8/1755 20130101;
B60W 10/08 20130101; B60W 2720/14 20130101; B60T 8/26 20130101;
B60W 2540/18 20130101; B60W 10/06 20130101; B60W 10/20 20130101;
B60W 2540/10 20130101; B60W 2720/406 20130101; B60W 10/14 20130101;
B60W 2520/10 20130101; B60T 8/245 20130101; B60T 8/246 20130101;
B60T 13/745 20130101; B60W 10/192 20130101; B60W 2710/182 20130101;
B60W 10/16 20130101 |
Class at
Publication: |
303/3 ; 303/140;
701/69 |
International
Class: |
B60W 30/045 20060101
B60W030/045; B60T 8/26 20060101 B60T008/26; B60T 13/74 20060101
B60T013/74; B60T 8/24 20060101 B60T008/24 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 28, 2010 |
JP |
2010-216335 |
Claims
1. A motion control system of a vehicle, comprising: a controller
that independently controls driving force and/or braking force of
each of four wheels; and a turning direction sensor that senses a
turning direction, wherein: the controller is provided with an
acceleration/deceleration command generator that generates an
acceleration/deceleration command based upon a sensed steering
angle and sensed vehicle speed and a driving force/braking force
distributor that determines the distribution of the driving force
or driving torque and/or the braking force or braking torque of
each wheel; and the driving force/braking force distributor
determines that it distributes more driving force or more driving
torque and/or more braking force or more braking torque to the
inside wheel in turning than the outside wheel in turning as to the
front wheels and distributes more driving force or more driving
torque and/or more braking force or more braking torque to the
outside wheel in turning than the inside wheel in turning as to the
rear wheels respectively based upon the acceleration/deceleration
command and the turning direction.
2. The motion control system of the vehicle according to claim 1,
wherein: the turning direction sensor senses the turning direction
based upon at least one of an input steering angle, a vehicular yaw
rate and vehicular lateral acceleration.
3. The motion control system of the vehicle according to claim 1,
wherein: the driving force/braking force distributor determines
such distribution that the driving torque and/or the braking torque
of the inside front wheel in turning and the driving torque and/or
the braking torque of the outside rear wheel in turning are
substantially equal.
4. The motion control system of the vehicle according to claim 1,
wherein: the driving force/braking force distributor determines
such distribution that the driving force and/or the braking force
of the inside front wheel in turning and the driving force and/or
the braking force of the outside rear wheel in turning are
substantially equal.
5. The motion control system of the vehicle according to claim 1,
comprising: a first hydraulic oil piping that communicates with the
left front wheel and the right rear wheel; and a second hydraulic
oil piping that communicates with the right front wheel and the
left rear wheel, wherein: the controller controls pressure in the
first hydraulic oil piping and pressure in the second hydraulic oil
piping.
6. The motion control system of the vehicle according to claim 5,
wherein: the controller makes such control that internal pressure
in the first hydraulic oil piping that communicates with the inside
front wheel in turning and the outside rear wheel in turning or the
second hydraulic oil piping is substantially the same.
7. The motion control system of the vehicle according to claim 1,
comprising: an electric motor that generates braking force or
braking torque, wherein: the controller is provided with a
regenerative device that regenerates electric power generated when
braking force or braking torque is generated by the electric
motor.
8. The motion control system of the vehicle according to claim 1,
wherein: the acceleration/deceleration command is generated to be
curved transition as time elapses in a diagram having vehicular
longitudinal acceleration on an axis of an abscissa and having
vehicular lateral acceleration on an axis of an ordinate.
9. The motion control system of the vehicle according to claim 1,
wherein: the acceleration/deceleration command is generated for the
vehicle to decelerate when lateral acceleration of the vehicle
increases and for the vehicle to accelerate when the lateral
acceleration of the vehicle decreases.
10. The motion control system of the vehicle according to claim 1,
wherein: the acceleration/deceleration command is generated for the
vehicle to decelerate when the steering angle of the vehicle
increases and for the vehicle to accelerate when the steering angle
of the vehicle decreases.
11. The motion control system of the vehicle according to claim 1,
wherein: the acceleration/deceleration command is generated based
upon lateral acceleration and a lateral jerk of the vehicle
respectively generated based upon the steering angle and the
vehicle speed of the vehicle and predetermined gain.
12. The motion control system of the vehicle according to claim 11,
wherein: the acceleration/deceleration command Gxc is generated by
calculating the following mathematical expression 1. G xc = - sgn (
G y G . y ) C xy 1 + T s G . y + G x_DC ( Mathematical expression 1
) ##EQU00021## (However, Gy: vehicular lateral acceleration,
Gy_dot: vehicular lateral jerk, Cxy: gain, T: first-order lag time
constant, s: Laplace operator, G.sub.x.sub.--.sub.nc: offset)
13. The motion control system of the vehicle according to claim 11,
wherein: the lateral jerk is calculated by differentiating lateral
acceleration estimated from a yaw rate and vehicle speed estimated
based upon the steering angle and the vehicle speed or sensed by a
yaw rate sensor or sensed by a lateral acceleration sensor by
time.
14. The motion control system of the vehicle according to claim 1,
wherein: the acceleration/deceleration command includes target
longitudinal acceleration and the target yaw moment respectively
generated based upon the steering angle and the vehicle speed.
15. The motion control system of the vehicle according to claim 14,
wherein: the target longitudinal acceleration is calculated based
upon lateral acceleration calculated based upon the steering angle
and the vehicle speed and a lateral jerk calculated based upon the
estimated lateral acceleration; and the target yaw moment is
calculated based upon the steering angle, the vehicle speed, a yaw
rate of the vehicle and a slip angle.
16. The motion control system of the vehicle according to claim 1,
wherein: the acceleration/deceleration command is provided with an
acceleration command and a deceleration command; the acceleration
command is turned zero when a braking operation command from a
driver is input; and the deceleration command is turned zero when
an accelerating operation command from the driver is input.
17. The motion control system of the vehicle according to claim 1,
wherein: the acceleration/deceleration command is turned zero by
external information including any of obstacle information,
preceding vehicle information and following vehicle information
sensed by an external information sensor.
18. The motion control system of the vehicle according to claim 1,
wherein: the acceleration/deceleration command is provided with an
acceleration command and a deceleration command; the acceleration
command is corrected to have a larger value when the grade of a
road surface detected by a road surface grade detector is ascent
than an acceleration command in running on a flat road and to have
a smaller value when the grade of a road surface is descent than
the acceleration command in running on the flat road; and the
deceleration command is corrected to have a smaller value when the
grade of a road surface detected by the road surface grade detector
is ascent than a value in the acceleration command in running on
the flat road and to have a larger value when the grade of a road
surface is decent than the value in the acceleration command in
running on the flat road.
19. The motion control system of the vehicle according to claim 1,
wherein: the driving force/braking force distributor makes such
correction based upon sensed or generated lateral acceleration
and/or sensed or generated longitudinal acceleration that
difference in driving force or driving torque and/or braking force
or braking torque between the inside front wheel in turning and the
outside front wheel and difference in driving force or driving
torque and/or braking force or braking torque between the outside
rear wheel in turning and the inside rear wheel are smaller.
20. The motion control system of the vehicle according to claim 1,
wherein: the controller is provided with a skid prevention device
having a skid prevention function that independently controls
driving force and/or braking force of each of the four wheels based
upon skid information calculated based upon the steering angle and
the vehicle speed or sensed; and the driving force/braking force
distributor stops the distribution control of driving force or
driving torque and/or braking force or braking torque to each wheel
when the skid prevention function is operated.
21. The motion control system of the vehicle according to claim 1,
comprising: a differential gear provided between the right and left
rear wheels, wherein: at least the rear wheels are driven by an
electric motor.
22. The motion control system of the vehicle according to claim 21,
wherein: the inside rear wheel in turning has longitudinal slip
ratio in a different direction from the outside rear wheel in
turning.
23. The motion control system of the vehicle according to claim 21,
wherein: the inside rear wheel in turning has longitudinal slip
ratio in a different direction from the outside rear wheel in
turning by controlling the revolution speed, the torque, apart of
the output or the whole output of the electric motor.
24. The motion control system of the vehicle according to claim 21,
wherein: it is determined that braking force or braking torque to
the rear wheel is distributed behind the front wheel.
25. The motion control system of the vehicle according to claim 11,
comprising: a differential gear provided between the right and left
rear wheels, wherein: at least the rear wheels are driven by an
electric motor.
26. The motion control system of the vehicle according to claim 25,
wherein: the inside rear wheel in turning has longitudinal slip
ratio in a different direction from the outside rear wheel in
turning.
27. The motion control system of the vehicle according to claim 25,
wherein: the inside rear wheel in turning has longitudinal slip
ratio in a different direction from the outside rear wheel in
turning by controlling the revolution speed, the torque, apart of
the output or the whole output of the electric motor.
28. The motion control system of the vehicle according to claim 25,
wherein: it is determined that braking force or braking torque to
the rear wheel is distributed behind the front wheel.
Description
TECHNICAL FIELD
[0001] The present invention relates to a vehicular motion control
system based upon braking force and driving force.
BACKGROUND ART
[0002] The enhancement of the controllability and the stability of
a vehicle is an eternal object for researchers related to a motion
of a vehicle. Currently, the following three methods are proposed
from Japan to the world.
(1) Four-Wheel Active Steer System
[0003] A patent literature 1 is based a four-wheel active steer
system provided with a front-wheel active steer means that applies
an auxiliary steering angle to a front wheel, a rear-wheel active
steer means that applies an auxiliary steering angle to a rear
wheel and a four-wheel active steer control means that instructs
both active steer means to apply the auxiliary steering angle to be
a desired vehicular behavior characteristic so as to provide the
four-wheel active steer system that applies no steering load onto a
driver, and discloses that a steered state sensing means that
senses a state steered by the driver, a response estimating means
that estimates a response of at least either of the front-wheel and
the rear-wheel active steer means and a response changing means
that changes the other response according to the variation of the
sensed steered state and the estimated one response are provided. A
nonpatent literature 1 discloses that both yawing and a transverse
motion can be optimized by actively steering both the front wheel
and the rear wheel. For example, the nonpatent literature 1
discloses that all yawing (turning round a vehicle), the
enhancement of a lateral acceleration response and the reduction of
a skid of a vehicle body can be all realized by turning the front
wheel by operating a handle at medium speed and also steering the
rear wheel in the same direction at the same time. Especially, a
nonpatent literature 8 discloses that immediately before steady
turning, that is, after a yaw rate required for turning is
acquired, the rear wheel is steered in phase and stability is
secured.
[0004] The four-wheel active steer systems disclosed in the patent
literature 1 and the nonpatent literature 1 are respectively
configured by respective actuators for actively steering the front
wheel and the rear wheel and two electronic control units (ECU).
The actuator for steering the front wheel is configured by parts
such as a motor to be a driving source, a deceleration mechanism, a
turning angle sensor, a locking mechanism and a spiral cable for
power supply. The actuator for steering the rear wheel is attached
to a suspension member and steers the rear wheel via a suspension
lower link after the rotation of a motor is converted to a
translation motion in the deceleration mechanism.
(2) Direct Yaw-Moment Control (DYC)
[0005] Besides, in a patent literature 2, it is disclosed that the
yaw moment is controlled by distributing driving force or braking
force between right and left wheels of a vehicle, a feed-forward
control device estimates a driving force distributed amount
.DELTA.T at which a yaw rate corresponding to a turned state of the
vehicle is acquired based upon engine torque, engine speed, vehicle
speed, a steering angle and lateral acceleration so as to make a
response and the precision of control compatible and feed-forward
controls left and right hydraulic clutches CL, CR in a driving
force distribution system. In the meantime, a feed-back control
device calculates a deviation between a normal yaw rate calculated
based upon vehicle speed and lateral acceleration and an actual yaw
rate sensed by a yaw rate sensor 10d and corrects the driving force
distribution amount .DELTA.T calculated in the driving force
distribution system so as to make the deviation converge on zero.
It is disclosed that even if the driving force distribution amount
becomes excessive by feed-forward control and a trend of oversteer
is caused in a vehicle, the trend of oversteer is eliminated by
feed-back control and a behavior of the vehicle can be stabilized
(refer to a nonpatent literature 2).
[0006] That is, a rear drive unit which is a DYC system and which
is disclosed in the patent literature 2 and the nonpatent
literature 2 is configured by parts such as a speed increasing unit
including a high-low clutch, a planetary gear and an oil pump, a
hypoid gear that converts a direction of drive, two right and left
electromagnetic clutches and a planetary gear so as to make the
distribution of torque between the right and left sides of a rear
wheel free.
(3) G-Vectoring
[0007] A method of generating a moving load between a front wheel
and a rear wheel by automatically accelerating or decelerating in a
link with a transverse motion by operating a handle and enhancing
the operability and the stability of a vehicle is also disclosed in
a nonpatent literature 3.
[0008] An acceleration/deceleration command value for automatically
accelerating or decelerating (target longitudinal acceleration
G.sub.xc) is acquired in the following mathematical expression
1.
[ Mathematical expression 1 ] G xc = - sgn ( G y G . y ) Cxy 1 + Ts
G . y + G x_DC ( Mathematical expression 1 ) ##EQU00001##
Basically, the above-mentioned command value complies with a simple
control rule that a value acquired by multiplying a lateral jerk
G.sub.y.sub.--.sub.dot by gain C.sub.xy and applying a first-order
lag is used for a longitudinal acceleration/deceleration
command.
[0009] However, Gy: vehicular lateral acceleration, Gy_dot (| y|):
vehicular lateral jerk, Cxy: gain, T: first-order lag time
constant, s: Laplace operator, G.sub.x.sub.DC: offset.
[0010] It is verified in a nonpatent literature 4 that hereby, a
part of linkage control strategy of a transverse motion and a
lengthwise motion of an expert driver can be simulated and the
enhancement of the operability and the stability of a vehicle can
be realized. G.sub.x.sub.--.sub.DC in this expression is a
deceleration component (an offset) not linked with a transverse
motion. The G.sub.x.sub.--.sub.DC is a term required in a case of
foreseen deceleration when a corner exists in front or when an
interval speed command is issued. Besides, sgn (signum) is a term
provided to acquire the above-mentioned operation both at a right
corner and at a left corner. Concretely, operation that speed is
decreased when steering is started and a turn is started,
deceleration is stopped in steady turning (because a lateral jerk
is zero) and speed is accelerated when return in steering is
started and in escape from a corner can be realized.
[0011] As in such control, synthetic acceleration (expressed with
G) of longitudinal acceleration and lateral acceleration is
vectored to have curved transition in the elapse of time in a
diagram having vehicular longitudinal acceleration on an axis of
abscissas and having vehicular lateral acceleration on an axis of
ordinates, the control is called G-Vectoring control.
CITATION LIST
Patent Literature
[0012] [Patent Literature 1] Japanese Unexamined Patent Application
Publication No. 2008-80840 [0013] [Patent Literature 2] Japanese
Unexamined Patent Application Publication No. Hei9 (1997)-309357
[0014] [Patent Literature 3] Japanese Unexamined Patent Application
Publication No. 2008-201358
Nonpatent Literature
[0014] [0015] [Nonpatent Literature 1] T. Katayama; Y. Anno; T.
Taneda; M. Sao; M. Imamura; S. Sekinaga; Y. Sato: Development of
four-wheel active steer, Society of Automotive Engineers of Japan,
Inc., Proc. before scientific lecture meeting, document No.:
20075281 No. 11-07 pp. 7-12, May, 2007. [0016] [Nonpatent
Literature 2] Shibahata, Y.; Tomari, T; and Kita, T.; SH-AWD:
Direct Yaw Control (DYC), 15. Aachener Kolloquium Fahrzeug-und
Motorentechinik, p. 1627, 1640, 1641, 2006. [0017] [Nonpatent
Literature 3] M. Yamakado, M. Abe: Improvement of Vehicle Agility
and Stability by G-Vectoring Control, Proc. of AVEC2008-080420.
[0018] [Nonpatent Literature 4] M. Yamakado, M. Abe: Proposal of
the longitudinal driver model in coordination with vehicle lateral
motion based upon jerk information, Review of Automotive
Engineering, Vol. 29, No. 4, October 2008, pp. 533 to 541. [0019]
[Nonpatent Literature 5] K. Mori; T. Eguchi; N. Irie: Enhancement
of operability by control over transition of steering rear wheel,
Society of Automotive Engineers of Japan, Automobile technology,
Vol. 44, No. 3, 1990
SUMMARY OF INVENTION
Technical Problem
[0020] In techniques disclosed in the patent literatures 1, 2 and
the nonpatent literatures 1, 2, the maneuverability of a vehicle is
enhanced by operating a steering actuator by electricity or oil
pressure and independently applying driving force to right and left
wheels, that is, applying energy to them.
[0021] Further, the weight of the vehicle increases when plural
intricate mechanisms are mounted in the vehicle and the cost of the
vehicle also increases. Besides, minute control tuning is required
to be executed in running tests to be suited to an individual
vehicle and this also increases the cost of the vehicle.
Especially, as in the DYC, interrupt by control is allowed
independent of a motion of the vehicle, the control has a degree of
freedom in the interrupt. As it is different depending upon a
condition of each motion in each vehicle at which timing and how
the yaw moment is to be applied, a man-hour of tuning is apt to
greatly increase.
[0022] In the meantime, control disclosed in the nonpatent
literatures 3, 4 is automatic control over a normal brake or a
normal accelerator, low-priced configuration can be expected, and
in addition, there is also no increase of weight. Besides, the
maneuverability of a vehicle can be enhanced, generating energy by
making regenerative control using an electric motor for a brake. In
addition, this control method is extracted from braking and
accelerating operation according to steering operation performed by
an expert driver as required and there is hardly a sense of
incompatibility even if interrupt is automatically made from a
normal area. The dynamical rationality of this control method and
the enhancement of operability and stability are demanded as a
result of simulation and a result of vehicle tests.
[0023] As acceleration and deceleration are controlled in linkage
of them so that the behavior of the vehicle suitably responds to
the steering operation of the driver, a slip angle of the vehicle
can be prevented from increasing as a result. Especially, the
control is effective to reduce so-called understeer in which a
radius of turning too increases for steering.
[0024] However, as a steering angle input to the vehicle and the
yaw moment applied to the vehicle are not directly controlled,
there is a problem that great effect is not necessarily acquired,
compared with four-wheel active steer disclosed in the patent
literature 1 and the nonpatent literature 1 and a DYC system
disclosed in the patent literature 2 and the nonpatent literature
2.
[0025] Besides, control disclosed in the nonpatent literatures 3, 4
has a problem that the effect of the transfer of a load and lateral
force by longitudinal force are deteriorated when a vehicle is
stabilized and control over the accelerating side is securely
required in a front-wheel-drive vehicle. This method shows effect
in escape from a corner, however, when stability is required in the
latter half of a condition of transition from the start of turning
to steady turning, the consistency of deceleration and acceleration
is not acquired and it is required to decrease gain in a range in
which stability can be secured.
[0026] An object of the present invention is to provide a
low-priced and light vehicular motion control system that enables
enhancing operability, stability and further, ride, comfort.
Solution to Problem
[0027] To achieve the object, the motion control system of a
vehicle according to the present invention is provided with a
control means that independently controls the driving force and/or
the braking force of each of four wheels and a turning direction
sensing means that senses a turning direction, the control means is
provided with an acceleration/deceleration command generation means
that generates an acceleration/deceleration command based upon a
sensed steering angle and sensed vehicle speed and a driving
force/braking force distribution means that determines the
distribution of driving force or driving torque and/or braking
force or braking torque of each wheel, and the driving
force/braking force distribution means determines so that more
driving force or more driving torque and/or more braking force or
more braking torque are/is distributed to the inside front wheel in
turning than the outside front wheel in turning based upon the
acceleration/deceleration command and the turning direction and
more driving force or more driving torque and/or more braking force
or more braking torque are/is distributed to the outside rear wheel
in turning than the inside rear wheel in turning based upon the
acceleration/deceleration command and the turning direction.
Advantageous Effects of Invention
[0028] The low-priced light vehicular motion control system that
enables enhancing operability, stability and further, ride comfort
can be realized.
BRIEF DESCRIPTION OF DRAWINGS
[0029] FIG. 1 shows the comparison between a normal vehicle and a
four-wheel active steer vehicle in a condition from linear running
to the beginning of turning;
[0030] FIG. 2 shows the comparison between the normal vehicle and
the four-wheel active steer vehicle in a condition from turning to
return to linear running;
[0031] FIG. 3 shows situations in which compliance steer is caused
by braking force and driving force;
[0032] FIG. 4 shows a situation in which compliance steer by
braking force to the inside of a front wheel is caused;
[0033] FIG. 5 shows a situation in which compliance steer by
driving force to the inside of the front wheel is caused;
[0034] FIG. 6 shows a situation from approach to a left corner to
escape of a vehicle to which G-Vectoring control is applied;
[0035] FIG. 7 shows time series data in a case of running shown in
FIG. 6;
[0036] FIG. 8 shows the comparison relating to the four-wheel
active steer vehicle, the distribution of braking force according
to the present invention and the distribution of braking
force/driving force according to the present invention in a
condition from linear running to the beginning of turning;
[0037] FIG. 9 shows the comparison relating to the four-wheel
active steer vehicle, the distribution of braking force according
to the present invention and the distribution of braking
force/driving force according to the present invention in a
condition from turning to return to linear running;
[0038] FIG. 10 shows the whole configuration of a first embodiment
of a motion control system of a vehicle according to the present
invention;
[0039] FIG. 11 shows vehicular lateral acceleration and an
estimated jerk respectively using a vehicle model;
[0040] FIG. 12 shows vehicular lateral acceleration, a jerk
respectively using a combined sensor and the output of a
G-Vectoring command;
[0041] FIG. 13 shows a concept of mutual complement by an estimated
signal and a sensed signal;
[0042] FIG. 14 shows control logic configuration of the motion
control system of the vehicle according to the present
invention;
[0043] FIG. 15 shows force applied to the vehicle, acceleration and
a yawing motion;
[0044] FIG. 16 shows the determination of the ratio .alpha. of
distribution to each wheel and the distribution of braking
force/driving force;
[0045] FIG. 17 shows time series data of the vehicle under control
according to the present invention in the case of running shown in
FIG. 6;
[0046] FIG. 18 shows the distribution of braking force and driving
force and a steering angle in the vehicle under the control
according to the present invention at each time shown in FIG.
17;
[0047] FIG. 19 shows time series data of the vehicle under
braking/driving force simultaneous distribution control according
to the present invention in the case of running shown in FIG.
6;
[0048] FIG. 20 shows braking/driving force simultaneous
distribution and a steering angle at each time shown in FIG. 19 in
the vehicle under the control according to the present
invention;
[0049] FIG. 21 shows time series data of the vehicle under braking
force/driving force distribution control according to the present
invention when a driver inputs an acceleration/deceleration command
in the case of running shown in FIG. 6;
[0050] FIG. 22 shows time series data of the vehicle under braking
force, braking/driving force simultaneous distribution control
according to the present invention when the driver inputs an
acceleration/deceleration command in the case of running shown in
FIG. 6;
[0051] FIG. 23 shows a vehicle model in full vehicle
simulation;
[0052] FIG. 24 shows results in comparison in a steering angle of
the full vehicle simulation;
[0053] FIG. 25 shows results in comparison in a vehicular locus of
the full vehicle simulation;
[0054] FIG. 26 shows the whole configuration of a second embodiment
of the motion control system of the vehicle according to the
present invention;
[0055] FIG. 27 shows the transfer of a load by longitudinal/lateral
acceleration and a characteristic of a tire;
[0056] FIG. 28 shows results (braking on turning) of an experiment
for verifying initial potential of the present invention;
[0057] FIG. 29 shows a condition and results of an experiment of
the present invention and conventional type control;
[0058] FIG. 30 compares vehicle speed of the present invention and
the conventional type control;
[0059] FIG. 31 compares the distribution of oil pressure to a brake
of the present invention and the conventional type control;
[0060] FIG. 32 compares the longitudinal acceleration and the
lateral acceleration of the present invention and the conventional
type control;
[0061] FIG. 33 compares a steering angle and yaw rate gain of the
present invention and the conventional type control;
[0062] FIG. 34 compares a roll rate and a pitch rate of the present
invention and the conventional type control;
[0063] FIG. 35 shows longitudinal acceleration, lateral
acceleration and a roll rate of the present invention;
[0064] FIG. 36 shows a condition and results of an experiment of
the present invention and the conventional type control;
[0065] FIG. 37 compares vehicle speed of the present invention and
the conventional type control;
[0066] FIG. 38 compares the distribution of oil pressure to the
brake of the present invention and the conventional type
control;
[0067] FIG. 39 compares slip ratio of the present invention and the
conventional type control;
[0068] FIG. 40 compares longitudinal acceleration and lateral
acceleration of the present invention and the conventional type
control;
[0069] FIG. 41 compares a steering angle and yaw rate gain of the
present invention and the conventional type control;
[0070] FIG. 42 shows the whole configuration of a third embodiment
of the motion control system of the vehicle according to the
present invention;
[0071] FIG. 43 shows a situation in which compliance steer is
caused when deceleration is applied to a rear wheel in the third
embodiment of the present invention;
[0072] FIG. 44 shows the configuration of a power train to the rear
wheels and right and left brakes of the rear wheels in the third
embodiment of the present invention;
[0073] FIG. 45 is an explanatory drawing related to velocity
vectors in a longitudinal direction in positions of the right and
left rear wheels in the vehicle that turns leftward in the third
embodiment of the present invention;
[0074] FIG. 46 shows a case that no braking force and no driving
force are applied to the right and left rear wheels that turn
leftward;
[0075] FIG. 47 shows a case that braking torque is applied to the
right rear wheel which is the outside rear wheel in turning;
[0076] FIG. 48 shows wheel speed (converted to peripheral velocity)
of the outside rear wheel and the inside rear wheel on a pressed
snowy road;
[0077] FIG. 49 shows a situation in which longitudinal force is
generated in the rear wheel when braking torque is applied to the
right rear wheel which is the outside rear wheel in turning;
[0078] FIG. 50 shows a best mode of the vehicle in the third
embodiment of the present invention;
[0079] FIG. 51 shows a case that G-Vectoring (proportional to a
lateral jerk) is applied to an acceleration/deceleration
command;
[0080] FIG. 52 shows a control mode at each timing of the vehicle
in the third embodiment of the present invention;
[0081] FIG. 53 shows a running scene on the inclined ground;
[0082] FIG. 54 shows a situation in which the vehicle descends on a
slope; and
[0083] FIG. 55 shows a feedback loop of longitudinal
acceleration.
DESCRIPTION OF EMBODIMENTS
[0084] In the present invention, a steering angle to be input to a
vehicle is required to be correctly controlled at each stage
including a stage of a start of turning from a straight line, a
stage of steady turning from the start of turning and a stage of
escape from the steady turning to the straight line without a
complex steering actuator.
[0085] Besides, especially in (i) a vehicle having a rear-wheel
longitudinal force toe-in characteristic using a multi-link
suspension and others and (ii) a vehicle provided with a
differential gear between rear right and left wheels respectively
recently often seen in a rear-wheel-drive vehicle, the management
of not only a steering angle but side torque via the differential
gear is required.
[0086] Concretely, a guideline for steering angle control at each
stage in four-wheel active steering will be described below and a
guideline of drive control by referring to the guideline will be
described below.
(1) Stage from a Straight Line to a Start of Turning
[0087] A largish steering angle is applied by applying additional
steering by control in addition to input from a driver and a rear
wheel is effective for so-called antiphase steering in which the
rear wheel is steered in a reverse direction to a front wheel to
acquire nimble feeling (a nimble response).
(2) Stage from the Start of Turning to Steady Turning
[0088] As a lateral acceleration response is deteriorated and a
slip angle of a vehicle body also increases when the antiphase
steering is kept, the additional steering by control over the front
and rear wheels is turned zero when steady turning is started.
(3) Stage from the Steady Turning to Escape
[0089] An additional steering angle is applied to the front wheel
so that a steering angle of the front wheel decreases prior to a
steering angle at which the driver returns a handle. The rear wheel
acquires a slip angle of a tire by being steered in phase with the
front wheel and more rear-wheel cornering force is generated. As in
such control, the moment to return from turning to linear running
increases in the vehicle, the control is effective to enhance
stability.
[0090] To acquire effects by the steering angle control (1) to (3)
without an actuator for steering, the present invention has
configuration that compliance steer caused by the compliance of
suspension applied to a passenger car so as to enhance the ride
comfort of the vehicle is actively controlled by braking force and
driving force. The compliance steer is basically caused because of
the shortage in rigidity of the suspension of the tire to braking
force and driving force, a steering angle is introrsely generated
because the tire is displaced forward for the vehicle when driving
force or driving torque is applied, when braking force or braking
torque is applied, the tire is displaced backward for the vehicle,
and a steering angle is extrorsely generated. Especially, as the
front wheel is provided with a steering mechanism, the front wheel
has more factors that cause the following compliance steer,
compared with the rear wheel fixed substantially in a traveling
direction of the vehicle body.
[0091] (i) Compliance steer caused by the torsional rigidity of a
steering column and the installation rigidity of a steering rack
for example even if a steering angle is fixed
[0092] (ii) Compliance steer in the wide sense in which a steering
angle on the driver's side increases and decreases by the moment
around a king pin axis generated by braking/driving torque and
which results from the shortage in rigidity of an arm (on the input
side) of the driver
[0093] In the present invention, these two factors are called
compliance steer in total.
[0094] As described above, the compliance steer is apt to be
interpreted as caused by an external factor, however, it can be
said that if only driving force or driving torque and braking force
or braking torque can be suitably distributed to four wheels at
each stage of (1) to (3), a steering angle can be controlled.
[0095] Concretely, a sensing means of a turning direction is
provided, based upon the accelerating/braking operation of a driver
or an acceleration/deceleration command (an acceleration command, a
deceleration command) from a control device or both, for the front
wheel, more driving force/driving torque and/or more braking
force/braking torque are/is distributed to the inside wheel in
turning, and for the rear wheel, more driving force/driving torque
and/or more braking force/braking torque are/is distributed to the
outside wheel in turning.
[0096] Besides, the above-mentioned distribution is required to be
changed according to each stage of (1) to (3) and an appropriate
controlled variable and switching timing every stage can be
acquired by using G-Vectoring control in which a control command is
determined based upon the variation of the stage of turning, that
is, the variation of lateral acceleration and a lateral jerk.
[0097] In the meantime, in the above-mentioned method of
distributing more driving force/driving torque or more braking
force/braking torque to the inside front wheel in turning, when a
load is displaced between the right and left wheels and a load of
the inside wheel decreases in a case that lateral acceleration
increases, a problem that the slip ratio of the inside wheel
increases and deceleration cannot be acquired occurs. This problem
can be avoided by correcting so that difference in driving
force/driving torque or braking force/braking torque between the
inside front wheel and the outside front wheel in turning and
difference in driving force/driving torque or braking force/braking
torque between the outside rear wheel and the inside rear wheel in
turning are smaller when a preset threshold in lateral acceleration
or longitudinal acceleration or both is exceeded. Or the problem
can be settled by correcting so that the difference in driving
force/driving torque or braking force/braking torque between the
inside front wheel and the outside front wheel in turning and the
difference in driving force/driving torque or braking force/braking
torque between the outside rear wheel and the inside rear wheel in
turning are smaller according to the increase of lateral
acceleration or longitudinal acceleration or both.
[0098] Further, as for (i) the vehicle having the rear-wheel
longitudinal force toe-in characteristic using the multi-link
suspension and others, though the tire is displaced backward for
the vehicle when braking force or braking torque is applied, a
steering angle is introrsely generated differently from the
above-mentioned normal vehicle.
[0099] Accordingly, the sensing means of a turning direction is
provided, based upon the accelerating/braking operation of the
driver or an acceleration/deceleration command (an acceleration
command, a deceleration command) from the control device or both,
for the front wheel, more driving force/driving torque and/or more
braking force/braking torque are/is distributed to the inside wheel
in turning, and for the rear wheel, more driving force/driving
torque and/or more braking force/braking torque are/is distributed
to the outside wheel in turning.
[0100] When more braking force/braking torque is distributed to the
inside front wheel in turning and more braking force/braking torque
is distributed to the outside rear wheel in turning, the front
wheel is directed in a toe-out direction on the side on which
turning is accelerated, the rear wheel is directed in a toe-in
direction on the stable side on which turning is stopped
respectively because of compliance steer, and the front wheel and
the rear wheel mutually interfere. Accordingly, in such a case, the
enhancement of turning round when turning is started and stable
transition to steady turning are enabled by controlling so that
first, braking force or braking torque is distributed to the inside
front wheel in turning and afterward, braking force or braking
torque is distributed to the outside rear wheel temporally behind
like the four-wheel active steer.
[0101] Besides, in (ii) the vehicle provided with the differential
gear between the rear right and left wheels, the sensing means of a
turning direction is provided, based upon the accelerating/braking
operation of the driver or an acceleration/deceleration command (an
acceleration command, a deceleration command) from the control
device or both, for the front wheel, more driving force/driving
torque and/or more braking force/braking torque are/is distributed
to the inside wheel in turning, and for the rear wheel, more
driving force/driving torque and/or more braking force/braking
torque are/is distributed to the outside wheel in turning.
[0102] When more braking force/braking torque is distributed to the
inside front wheel in turning and more braking force/braking torque
is distributed to the outside rear wheel in turning, driving force
or driving torque is caused inside turning when braking force or
braking torque is applied to the outside wheel in turning because
the inside and the outside rear wheels are coupled by the
differential gear.
[0103] Because of compliance steer, the front wheel is directed in
the toe-out direction (in a direction in which a steering angle
increases) on the side on which turning is accelerated, the rear
wheel is directed in the toe-in direction on the stable side on
which turning is stopped, and the front wheel and the rear wheel
mutually interfere. Accordingly, in such a case, the enhancement of
turning round when turning is started and stable transition to
steady turning are enabled by controlling so that first, more
braking force/braking torque is distributed to the inside front
wheel in turning and afterward, more braking force/braking torque
is distributed to the outside rear wheel temporally behind like the
four-wheel active steer.
[0104] First, the basic concept of a means for settling the problem
will be described and afterward, the means will be more described
in detail. Next, two embodiments will be described in detail.
Further, the effects of the present invention will be verified in
computer simulation and results verified in a vehicle test will be
described.
<Basic Concept of the Present Invention>
[0105] Steering angle control from four-wheel active steer control,
compliance steer by braking force/driving force and
acceleration/deceleration control (G-Vectoring control) linked with
a lateral motion will be described below and the basic concept of
the present invention in which these are organically combined will
be described below.
"Examination from a Viewpoint of Four-Wheel Active Steer
Control"
[0106] First, a general method of steering angle control for
enhancing the operability and the stability of a vehicle will be
described, referring to the nonpatent literature 1.
[0107] FIG. 1(a) shows a normal vehicle 1000 provided with no
steering angle control mechanism, FIG. 1(b) shows a four-wheel
active steer vehicle 1100, and both show the beginning of turning
from a linear state to a turned state (leftward turning).
[0108] In the normal vehicle 1000, a left front wheel 1011, a right
front wheel 1012, a left rear wheel 1013 and a right rear wheel
1014 are suspended by a left front-wheel suspension 1007, a right
front-wheel suspension 1008, a right rear-wheel suspension 1009 and
a left rear-wheel suspension 1010. A steering angle input from a
handle 1001 by a driver is transmitted to left and right knuckle
arms 1003, 1004 via each tie rod 1005 through a gear box 1006 of a
steering shaft 1002 and is realized as a steering angle
.delta..
[0109] In the meantime, in the four-wheel active steer vehicle
1100, a left front wheel 1111, a right front wheel 1112, a right
rear wheel 1113 and a left rear wheel 1114 are suspended by a left
front-wheel suspension 1107, a right front-wheel suspension 1108, a
right rear-wheel suspension 1109 and a left rear-wheel suspension
1110. The four-wheel active steer vehicle 1100 shown in FIG. 1(b)
is a so-called steer-by-wire (SBW) vehicle and a steering angle
input by the driver of a handle unit 1101 is input to a steering
controller 1120 via a steering angle sensor. The steering
controller 1120 controls a steering angle of the front wheel via
left and right knuckle arms 1103, 1104 of the front wheels via each
tie rod 1105 through a gear box 1106 of a steering shaft 1102 of
the front wheel according to the input and controls a steering
angle of the rear wheel via left and right knuckle arms 1123, 1124
of the rear wheels via each tie rod 1125 through a gear box 1126 of
a steering shaft 1112 of the rear wheel according to the input.
[0110] At the beginning of turning, to enhance turning round of the
vehicle, the yaw moment applied to the vehicle is required to be
increased. Therefore, the cornering force of the rear wheel can be
effectively decreased by increasing a steering angle of the front
wheel, increasing the cornering force of the front wheel, steering
the rear wheel in a reverse direction to the front wheel and
decreasing a slip angle of the rear wheel. As the actual yaw moment
onto the vehicle is determined by difference between the turning
moment by the cornering force of the front wheel and the moment on
the return side by the cornering force of the rear wheel, turning
round is enhanced by such control.
[0111] In the four-wheel active steer vehicle shown in FIG. 1 (b)
control is made so that a steering angle increases by
.delta..sub.f.sub.--.sub.AFS.sub.--.sub.A, compared with the normal
wheel shown in FIG. 1 (a) in which the front wheel is steered by
.delta. and control is made so that a steering angle increases by
.delta..sub.r.sub.--.sub.ARS.sub.--.sub.A in a reverse direction
(in an opposite phase) to the front wheel, compared with the normal
vehicle shown in FIG. 1 (a) in which no rear wheel is steered.
[0112] Next, four-wheel active steer control in a return from
turning to linear running will be described, referring to FIG.
2.
[0113] As FIG. 2 has the same configuration as that in FIG. 1, the
reference numerals showing each configuration (the numerals and
leader lines) are omitted.
[0114] In escape from turning to linear running, a turning motion
is required to be promptly converged and the yaw moment on the
return side applied to the vehicle is required to be increased.
Therefore, the cornering force of the rear wheel can be effectively
increased by decreasing a steering angle of the front wheel,
decreasing the cornering force of the front wheel, steering the
rear wheel in the same direction as the front wheel and increasing
a slip angle of the rear wheel. Returnability from a turning motion
to a direct advance is enhanced by offsetting the turning moment by
the cornering force of the front wheel against the moment on the
return side by the cornering force of the rear wheel.
[0115] In the four-wheel active steer vehicle shown in FIG. 2 (b)
control is made so that a steering angle decreases by
.delta..sub.f.sub.--.sub.AFS.sub.--.sub.S, compared with the normal
vehicle shown in FIG. 2(a) in which the front wheel is steered by
.delta. and control is made so that the rear wheel is steered by
.delta..sub.r.sub.--.sub.ARS.sub.--.sub.S in the same direction (in
phase) as (with) the front wheel, compared with the normal vehicle
shown in FIG. 2(a) in which no rear wheel is steered.
[0116] For control for enhancing the operability and the stability
of the four-wheel active steer vehicle, the basic concept that to
enhance the operability, the front wheel is more turned and the
rear wheel is turned in the reverse direction (in the opposite
phase) to the front wheel and to enhance the stability, the front
wheel is less turned and the rear wheel is turned in the same
direction (in phase) as (with) the front wheel has been
described.
"Compliance Steer"
[0117] Next, compliance steer by braking force and driving force
will be described, referring to FIGS. 3 to 5. As described in a
nonpatent literature 5 (M. Abe, H. Osawa: Automobile
maneuverability enhancing technology, 5.2 Suspension
characteristics and driving stability and 5.2.1 Variation of toe
angle and driving stability, pp. 84-85 in Chap. 5, Suspension and
vehicular maneuverability of Automotive engineering series 4 edited
by Society of Automotive Engineers of Japan and published by
Asakura Shoten, 1998), when lateral force such as cornering force
and longitudinal force such as braking force and driving force are
applied to the suspension, the variation of a toe angle occurs by
the elastic deformation of a rubber bushing and a link (as
compliance steer by lateral force is smaller than that by
longitudinal force and the variation of the toe angle occurs
independent of whether control according to the present invention
is made or not, it is not discussed in detail).
<Rear Wheel>
[0118] FIG. 3 shows the variation of a toe angle using the right
rear wheel 1014 of the normal vehicle 1000. The right rear wheel
1014 is suspended by the right rear-wheel suspension 1010 from the
vehicle, however, when braking force F.sub.xB is applied to the
center of the ground touched to the right rear wheel 1014 and
distance from the center to a mobile bearing on the side of the
vehicle body of a suspension link 1020 is 1.sub.s, the moment
equivalent to F.sub.xB.times.1.sub.s is applied to the right rear
wheel 1014. The suspension link 1020 is supported by a front mobile
bearing bush 1030 on the side of the vehicle body and a rear mobile
bearing bush 1040 on the side of the vehicle body, however, as
these supporting parts have compliance, an extrorse (toe-out)
compliance steer angle .delta..sub.xB is caused in the right rear
wheel as a result. Similarly, when driving force F.sub.xT is
applied to the right rear wheel 1014, an introrse (toe-in)
compliance steer angle .delta..sub.xT is caused.
[0119] According to the nonpatent literature 5, these steer angles
are approximately 0.5.degree. outside to 0.5.degree. inside/980 N
(braking force). In a torsion beam type suspension for example for
a low-cost vehicle that cannot have a special link configuration,
toe-out (in a direction shown in FIG. 3) occurs. An object of the
present invention is to realize technique and a low-priced and
light system that enable enhancing operability and stability with
sufficient effects and a vehicle to be an object is mainly a
low-priced vehicle, that is, having a toe-out characteristic.
Therefore, in this embodiment, compliance steer is made act in a
direction of toe-out by braking force and in a direction of toe-in
by driving force.
[0120] As a result, the above-mentioned is arranged as follows:
[0121] Braking force: steering angle in direction of toe-out [0122]
Driving force: steering angle in direction of toe-in
<Front Wheel>
[0123] Next, the front wheel will be described referring to FIG. 4.
In this case, braking force F.sub.xB.sub.--.sub.f shall be applied
to only the left front wheel 1011.
[0124] Basically, the front wheel shown in FIG. 4 is the same as
the rear wheel shown in FIG. 3, however, as the front wheel is a
steered wheel, it has a degree of freedom of turning around a king
pin axis 1200. Further, the left front wheel also mechanically
connects with the left front wheel 1011 via a steering mechanism.
When distance from the center of the wheel to the king pin axis
1200 is 1.sub.kp, the moment in the direction of toe-out equivalent
to F.sub.xB.sub.--.sub.f.times.1.sub.kp is applied around the king
pin axis. When distance from the king pin axis to a steering rack
is 1.sub.1, axial force equivalent to
F.sub.B.sub.--.sub.1=F.sub.xB.sub.--.sub.f.times.1.sub.kp/1.sub.l
is applied to the steering rack. There is a case that an angle
steered by a driver is extra turned by .delta..sub.xB by this
force. Besides, even if the driver completely holds a steering
angle, a steering angle .delta..sub.xB.sub.--.sub.f in the
direction of toe-in is caused like the rear wheel because of the
torsional rigidity of a steering shaft or the deflection of each
bush. At this time, .delta..sub.xB.sub.--.sub.f is also caused on
the left side of the front wheel connected via the steering
mechanism.
[0125] Similarly, as shown in FIG. 5, when driving force
F.sub.xT.sub.--.sub.f is applied to only the left front wheel 1011,
a steering angle .delta..sub.xT.sub.--.sub.f in a direction of
toe-out is generated. At this time, .delta..sub.xT.sub.--.sub.f is
also generated on the left side of the front wheel connected via
the steering mechanism.
[0126] As a result, the above-mentioned is arranged as follows:
[0127] Braking force: steering angle in direction of toe-in [0128]
Driving force: steering angle in direction of toe-out
"G-Vectoring Control"
[0129] Next, acceleration/deceleration control which can enhance
operability and stability and which is linked with a transverse
motion will be described. A guideline of acceleration/deceleration
control linked with a transverse motion is described in a nonpatent
literature 3 for example.
[0130] As shown in the mathematical expression 1, the guideline is
basically a simple control rule that a value acquired by
multiplying a lateral jerk G.sub.y.sub.--.sub.dot by gain C.sub.xy
and applying a first-order lag is used for a longitudinal
acceleration/deceleration command. That is, the
acceleration/deceleration command is generated based upon vehicular
lateral acceleration generated based upon a steering angle and
vehicle speed of the vehicle, a lateral jerk and predetermined gain
and more concretely, is acquired in the mathematical expression
1.
[0131] Hereby, it is verified in the nonpatent literature 2 that a
part of linkage control strategy of a transverse motion and a
longitudinal motion of an expert driver can be simulated.
G.sub.x.sub.--.sub.DC in the mathematical expression 1 is a
deceleration component not related to a lateral motion. It is a
term required for foreseen deceleration when a corner exists in
front or when an interval speed command is issued. Besides, an sgn
(signum) term is provided to acquire the above-mentioned operation
at both a right corner and a left corner. Concretely, operation
that deceleration is made in the start of steering, in steady
turning, deceleration is stopped (because a lateral jerk becomes
zero) and acceleration is made in escape from a corner when return
is started can be realized. Acceleration/deceleration according to
a lateral jerk means that deceleration is made when lateral
acceleration increases and acceleration is made when lateral
acceleration decreases.
[0132] Such control is called G-Vectoring control because synthetic
acceleration (expressed with G) of longitudinal acceleration and
lateral acceleration is vectored so that the synthetic acceleration
shows curved (circular) transition as time elapses in a diagram
having vehicular longitudinal acceleration on an axis of abscissas
and having vehicular lateral acceleration on an axis of
ordinates.
[0133] As for a vehicular motion when the control shown in the
mathematical expression 1 is applied, supposed concrete running
will be described below.
[0134] FIG. 6 shows a direct advance route A, a transient interval
B, a steady turning interval C, a transient interval D and a direct
advance interval E, which are intervals when a general running
scene including approach to a corner and escape from the corner is
supposed. At this time, no operation for accelerating or
decelerating by a driver shall be made.
[0135] FIG. 7 shows a steering angle, lateral acceleration, a
lateral jerk, an acceleration/deceleration command calculated in
the mathematical expression 1 and braking force/driving force to
four wheels in the shape of a time history waveform. Though the
following is described in detail later, braking force/driving force
is distributed between the outside front wheel and the inside front
wheel and between outside rear wheel and the inside rear wheel to
be the same values between the inside and the outside.
Braking/driving force is a generic name of force generated in a
vehicular longitudinal direction of each wheel, braking force is
defined as force in a direction in which the vehicle is
decelerated, and driving force is defined as force in a direction
in which the vehicle is accelerated.
[0136] First, a vehicle enters a corner from the direct advance
interval A. In the transient interval B (points 1 to 3), as a
driver gradually turns the handle, lateral acceleration G.sub.y of
the vehicle increases. A lateral jerk G.sub.y.sub.--.sub.dot has a
positive value while lateral acceleration in the vicinity of the
point 2 increases (returns to zero at the time of the point 3 at
which the increase of lateral acceleration is finished). At this
time, as lateral acceleration G.sub.y increases, a deceleration
(G.sub.xc is negative) command is generated in the controlled
vehicle according to the mathematical expression 1. Hereby, braking
force (a minus sign) of the substantial same dimension is applied
to the outside front wheel, the inside front wheel, the outside
rear wheel and the inside rear wheel.
[0137] Afterward, when the vehicle enters the steady turning
interval C (points 3 to 5), the driver stops more turning the
handle and keeps a steering angle fixed. At this time, as a lateral
jerk G.sub.y.sub.--.sub.dot is zero, an acceleration/deceleration
command G.sub.xc is zero. Therefore, braking force/driving force to
each wheel is turned zero.
[0138] Next, in the transient interval D (points 5 to 7), the
lateral acceleration G.sub.y of the vehicle decreases by operation
for returning the handle by the driver. At this time, a lateral
jerk G.sub.y.sub.--.sub.dot of the vehicle is negative and an
acceleration command G.sub.xc is generated in the controlled
vehicle according to the mathematical expression 1. Hereby, driving
force (a plus sign) of the substantial same dimension is applied to
the outside front wheel, the inside front wheel, the outside rear
wheel and the inside rear wheel.
[0139] Besides, in the direct advance interval E, as a lateral jerk
G.sub.y is zero and a lateral jerk G.sub.y.sub.--.sub.dot is also
zero, no acceleration/deceleration control is made. As described
above, from the point 1 at which steering is started to the point
3, the vehicle is decelerated, during steady turning (the points 3
to 5), deceleration is stopped, and from the point 5 at which
turning back is started to escape from the corner (the point 7),
the vehicle is accelerated. As described above, when G-Vectoring
control is applied to the vehicle, an acceleration/deceleration
motion linked with a lateral motion can be realized if only the
driver steers for turning.
[0140] Besides, when this motion is expressed in a "g-g" diagram
showing longitudinal acceleration on an axis of abscissas, showing
lateral acceleration on an axis of ordinates and showing a mode of
acceleration caused in the vehicle, the motion is a characteristic
motion in which a smooth circular curve is drawn. An
acceleration/deceleration command according to the present
invention is generated to be a curved transition in the diagram as
time elapses. The curved transition shows clockwise transition at a
left corner as shown in FIG. 6, shows inverted transition based
upon the axis of G.sub.x at a right corner, and a direction of the
transition is counterclockwise. In such transition, a pitching
motion caused in the vehicle by longitudinal acceleration and a
roll motion caused by lateral acceleration are suitably linked and
peak values of a roll rate and a pitch rate are reduced.
[0141] The above-mentioned is arranged as follows: [0142] Interval
from linear running to beginning of turning:
deceleration->braking force [0143] From turning to return to
linear running: acceleration->driving force
[0144] The steering angle control for enhancing operability and
stability, the compliance steer by braking force/driving force and
the acceleration/deceleration control (the G-Vectoring control)
linked with a lateral motion have been described. Compliance steer
control by the distribution of braking force/driving force will be
described below.
[0145] A method of realizing the basic concept for enhancing
operability and stability in the above-mentioned four-wheel active
steer vehicle by distributing braking force/driving force will be
described referring to FIGS. 8 and 9 below.
[0146] As described above, for control for enhancing operability
and stability in the four-wheel active steer vehicle, the following
basic rule can be given. [0147] To enhance operability, the front
wheel is more turned and the rear wheel is turned in a reverse
direction (out of phase) to (with) the front wheel. [0148] To
enhance stability, the front wheel is turned back and the rear
wheel is turned in the same direction (in phase) as (with) the
front wheel.
[0149] FIGS. 8A, 8B and 8C show situations where the four-wheel
active steer vehicle and the vehicle to which the present invention
is applied and to which the distribution of braking force/driving
force is applied are respectively operated in a period from linear
running to the beginning of turning.
[0150] FIG. 8 (a) shows a condition in which the four-wheel active
steer vehicle is operated as in FIG. 2 (b), the front wheel is more
turned and the rear wheel is turned in a reverse direction (out of
phase) to (with) the front wheel.
[0151] In the meantime, FIG. 8 (b) shows the vehicle to which the
present invention is applied and to which the distribution of
braking force/driving force is applied. G-Vectoring control is
applied to the vehicle, a deceleration command is issued in the
interval from linear running to the beginning of turning, and
braking force is generated.
[0152] In the present invention, the sensing means of a turning
direction is provided and as shown in FIG. 8 (b), a braking device
is controlled so that greater braking force is generated in the
inside front wheel in turning than in the outside front wheel in
turning (in this example, braking force to the outside wheel in
turning is set to zero).
[0153] Hereby, a compliance steer angle on the toe-in side of the
front wheels is generated as in FIG. 8 (a). Further, the braking
device is controlled so that greater braking force is generated in
the outside rear wheel in turning than in the inside rear wheel in
turning (in this example, braking force to the inside wheel in
turning is set to zero).
[0154] Hereby, a compliance steer angle on the toe-out side is
generated in only the outside rear wheel as in FIG. 8(a).
[0155] Besides, FIG. 8 (c) shows the vehicle to which the present
invention is applied and to which the distribution of braking
force/driving force is applied. G-Vectoring control is applied to
the vehicle, in the interval from linear running to the beginning
of turning, a deceleration command is issued, and braking force is
generated.
[0156] In the present invention, the sensing means of a turning
direction is provided and as shown in FIG. 8(c), the braking device
or an electric regenerative braking device is controlled so that
greater braking force is generated in the inside front wheel in
turning than in the outside front wheel in turning. The
regenerative braking device regenerates electric power generated
when braking force or braking torque is generated by an electric
motor.
[0157] Driving force (negative braking force, therefore, it can be
considered that the driving force is smaller braking force than in
the inside front wheel in consideration of a sign) is distributed
to the outside front wheel in turning (the right front wheel) by
electric power from the regenerative braking device or electric
power from a battery or motive power from an internal combustion
engine.
[0158] Hereby, a greater compliance steer angle on the toe-in side
of the front wheels than the compliance steer angle in FIG. 8(b) in
which only braking force is distributed is generated. Further, the
braking device or the electric regenerative braking device is
controlled so that greater braking force is generated in the
outside rear wheel in turning than in the inside rear wheel in
turning. Driving force (negative braking force, therefore, it can
be considered that the driving force is smaller braking force than
in the outside rear wheel in consideration of a sign) is
distributed to the inside rear wheel in turning (the left rear
wheel) by electric power from the regenerative braking device or
electric power from the battery or motive power from the internal
combustion engine.
[0159] Hereby, as in FIG. 8(a), a compliance steer angle on the
toe-out side is generated in both rear wheels.
[0160] Naturally, in FIG. 8(c), as driving force or driving torque
is applied to the vehicle, adjustment is required to be made so
that deceleration instructed by a G-Vectoring control device based
upon difference between braking force and driving force can be
realized.
[0161] As described above, the similar steering control effect to
that of the four-wheel active steer can be also acquired by
distributing braking force based upon a G-Vectoring deceleration
command value to the diagonal wheels (more braking force is applied
to the inside front wheel and more braking force is applied to the
outside rear wheel (also in consideration of the sign) in addition
to the enhancement of operability by G-Vectoring and operability,
especially a yaw response can be more enhanced.
[0162] FIGS. 9A, 9B and 9C show situations where the four-wheel
active steer vehicle and the vehicle to which the present invention
is applied and to which the distribution of braking force/driving
force is applied in a period from turning to return to linear
running are operated.
[0163] FIG. 9(a) shows a condition in which the four-wheel active
steer vehicle is operated as in FIG. 3(b), the front wheel is
turned back and the rear wheel is turned in the same direction (in
phase) as (with) the front wheel.
[0164] In the meantime, FIG. 9(b) shows the vehicle to which the
present invention is applied and to which the distribution of
braking force/driving force is applied. G-Vectoring control is
applied to the vehicle, in a period from turning to return to
linear running, an acceleration command is issued, and driving
force is generated.
[0165] In the present invention, the sensing means of a turning
direction is provided and as shown in FIG. 9(b), a drive unit is
controlled so that greater driving force is generated in the inside
front wheel in turning than in the outside front wheel in turning
(in this example, driving force to the outside wheel in turning is
set to zero).
[0166] Hereby, a compliance steer angle on the toe-out side of the
front wheels is generated as in FIG. 9(a). Further, the drive unit
is controlled so that greater driving force is generated in the
outside rear wheel in turning than in the inside rear wheel in
turning (in this example, driving force inside turning is set to
zero).
[0167] Hereby, a compliance steer angle on the toe-in side (in
phase) is generated in only the outside rear wheel as in FIG.
9(a).
[0168] Besides, FIG. 9(c) shows the vehicle to which the present
invention is applied and to which the distribution of braking
force/driving force is applied. G-Vectoring control is applied to
the vehicle, in a period from turning to return to linear running,
an acceleration command is issued, and driving force is
generated.
[0169] In the present invention, the sensing means of a turning
direction is provided and as shown in FIG. 9(c), the drive unit is
controlled so that greater driving force is generated in the inside
front wheel in turning than in the outside front wheel in turning.
Besides, braking force (negative driving force, therefore, it can
be considered that the braking force is smaller driving force than
in the inside front wheel in consideration of the sign) is
distributed to the outside front wheel in turning (the right front
wheel). To generate braking force or braking torque, the braking
device or the electric regenerative braking device may be also
controlled. The regenerative braking device regenerates electric
power generated when braking force or braking torque is generated
by the electric motor.
[0170] Hereby, a greater compliance steer angle on the toe-out side
of the front wheels than that in FIG. 9(b) in which only driving
force is distributed is generated. Further, the drive unit is
controlled so that greater driving force is generated in the
outside rear wheel in turning than in the inside rear wheel in
turning.
[0171] Besides, braking force (negative driving force, therefore,
it can be considered that the braking force is smaller driving
force than in the outside rear wheel in consideration of the sign)
is distributed to the inside rear wheel in turning (the left rear
wheel). To generate braking force or braking torque, the braking
device or the electric regenerative braking device may be also
controlled. Hereby, a compliance steer angle on the toe-in side is
generated in both rear wheels as in FIG. 8 (a).
[0172] Naturally, in FIG. 9 (c), as driving force or driving torque
is applied to the vehicle, adjustment is required to be made so
that deceleration instructed by the G-Vectoring control device
based upon difference between driving force and braking force can
be realized.
[0173] As described above, the similar steering control effects to
the four-wheel active steer can be also acquired by distributing
driving force based upon a G-Vectoring deceleration command value
to the diagonal wheels (more to the inside front wheel and more to
the outside rear wheel) in addition to the enhancement of stability
by G-Vectoring and stability can be more enhanced.
[0174] The example that braking force or driving force is
controlled based upon an acceleration/deceleration command value by
G-Vectoring control is described above. In the meantime, when a
driver operates a brake in the interval from linear running to the
beginning of turning or when the driver operates an accelerator in
return from turning to linear running, the similar steering control
effects to the four-wheel active steer can be also acquired by
distributing braking force/driving force to the diagonal wheels
(more to the inside front wheel and more to the outside rear wheel)
as described above and operability and stability can be more
enhanced.
[0175] The above-mentioned is the main points and the basic concept
of the present invention for realizing the technique and the system
that enable the enhancement of operability and stability with
sufficient effects in the low-priced light system.
[0176] Next, two embodiments will be described in detail.
First Embodiment
[0177] FIG. 10 shows the whole configuration of a first embodiment
of the vehicular motion control system according to the present
invention.
[0178] In this embodiment, a vehicle 0 is configured by a so-called
by-wire system and no mechanical coupling part exists between a
driver and a steering mechanism, an acceleration mechanism or a
deceleration mechanism.
<Driving>
[0179] The vehicle 0 is a four-wheel-drive vehicle (an all wheel
drive (AWD) vehicle) where a left rear wheel 63 is driven by a left
rear-wheel motor 1, a right rear wheel 64 is driven by a right
rear-wheel motor 2, a left front wheel 61 is driven by a left
front-wheel motor 121 and a right front wheel 62 is driven by a
right front-wheel motor 122.
[0180] The vehicle has such configuration that the driving force
and the braking force of four wheels can be freely controlled by
combining with four-wheel independent brakes described later for a
most suitable example showing the present invention especially for
difference in a power source such as an electric motor and an
internal combustion engine. The configuration will be described in
detail below.
[0181] A brake rotor, a rotor for sensing wheel speed and a wheel
speed pickup provided on the side of the vehicle are respectively
mounted on the left front wheel 61, the right front wheel 62, the
left rear wheel 63 and the right rear wheel 64 so that the speed of
each wheel can be sensed. The quantity depressed by the driver of
an accelerator pedal 10 is sensed by an accelerator position sensor
31 and is operated in a central controller 40 which is a control
means via a pedal controller 48. The central controller 40
independently controls the driving force and/or the braking force
of each of the four wheels and in the operation, diagonal torque
distribution information for enhancing operability and stability as
the object of the present invention is also included. A power train
controller 46 controls the output of the left rear-wheel motor 1,
the right rear-wheel motor 2, the left front-wheel motor 121 and
the right front-wheel motor 122 according to this quantity.
[0182] An accelerator reaction motor 51 is also connected to the
accelerator pedal 10 and the reaction is controlled based upon a
command based upon the operation from the central controller 40 by
the pedal controller 48.
<Braking>
[0183] The brake rotor is respectively arranged on the left front
wheel 61, the right front wheel 62, the left rear wheel 63 and the
right rear wheel 64 and a caliper that decelerates the wheel by
holding the brake rotor between pads (not shown) is mounted on the
side of a vehicle body. A brake system is an electric type provided
with the electric motor every caliper.
[0184] The respective calipers are controlled basically based upon
the command based upon the operation from the central controller 40
by a brake controller 451 (for the left front wheel), a brake
controller 452 (for the right front wheel) and a brake controller
453 (for the rear wheels). A brake pedal reaction motor 52 is
connected to a brake pedal 11 and the reaction is controlled based
upon a command based upon operation from the central controller 40
by the pedal controller 48.
<Joint Control of Braking/Driving>
[0185] In the present invention, diagonal distribution is made to
enhance operability and stability, and different braking force and
different driving force are generated between the right and left
wheels. Besides, to further enhance operability when turning is
started for example, such joint control of braking/driving that
braking torque for the inside front wheel that creates the toe-in
of the front wheel is electrically regenerated, driving torque is
applied to the inside rear wheel using this electric power, the
inside wheels including the inside rear wheel are turned toe-in
using compliance steer, braking torque for the outside rear wheel
that creates the toe-out of the outside rear wheel is electrically
regenerated, driving torque is applied to the outside front wheel
using this electric power and the toe-in of the front wheels is
more strengthened is made.
[0186] As for a joint control command in such a situation, the
central controller 40 synthetically determines the command and the
command is suitably controlled via the brake controller 451 (for
the left front wheel), the brake controller 452 (for the right
front wheel), the brake controller 453 (for the rear wheels), the
power train controller 46, the left rear-wheel motor 1, the right
rear-wheel motor 2, the left front-wheel motor 121 and the right
front-wheel motor 122.
<Steering>
[0187] A steering system of the vehicle 0 has steer-by-wire
structure where no mechanical coupling part exists between a
steering angle applied by the driver and a tire turning angle. The
steering system is configured by a power steering 7 including a
steering angle sensor (not shown) inside, a steering wheel 16, a
driver steered angle sensor 33 and a steering controller 44. The
quantity steered by the driver of the steering wheel 16 is sensed
by the driver steered angle sensor 33 and is operated in the
central controller 40 via the steering controller 44. The steering
controller 44 controls the power steering 7 according to this
quantity.
[0188] A steer reaction motor 53 is also connected to the steering
wheel 16 and the reaction is controlled based upon a command based
upon the operation from the central controller 40 by the steering
controller 44.
[0189] The quantity depressed by the driver of the brake pedal 11
is sensed by a brake pedal position sensor 32 and is operated in
the central controller 40 via the pedal controller 48.
<Sensor>
[0190] Next, a group of motion sensors according to the present
invention will be described.
[0191] The sensors that measure a motion of the vehicle in this
embodiment are provided with an absolute vehicle speed meter, a yaw
rate sensor, an acceleration sensor and others. In addition, as for
vehicle speed and a yaw rate, an estimate by a wheel speed sensor
and as to the yaw rate and lateral acceleration and an estimate
using vehicle speed, a steering angle and a vehicular motion model
are simultaneously performed.
[0192] A millimeter wave ground vehicle speed sensor 70 which is an
external information sensing means is mounted in the vehicle 0,
senses obstacle information, preceding vehicle information and
following vehicle information, and can independently sense
longitudinal velocity V.sub.x and lateral velocity V.sub.y.
Besides, the wheel speed of each wheel is input to the brake
controllers 451, 452 as described above. Absolute vehicle speed can
be estimated by balancing the speed of the front wheel (the
non-driving wheel) based upon the wheel speed of the four
wheels.
[0193] In the present invention, the absolute vehicle speed
(V.sub.x) can be precisely measured by applying a signal from the
acceleration sensor that senses the wheel speed and acceleration in
a longitudinal direction of the vehicle using a method disclosed in
Japanese Unexamined Patent Application Publication No. 1993-16789
even if the wheel speed of the four wheels falls at the same
time.
[0194] Besides, such configuration that a yaw rate of the vehicle
body is estimated by calculating difference between the wheel speed
of the right and left front wheels (the non-driving wheels) is also
included and the robustness of a sensing signal is enhanced. These
signals are ordinarily monitored in the central controller 40 as
shared information. Estimated absolute vehicle speed is compared
with a signal from the millimeter wave ground vehicle speed sensor
70, the signal is referred to, and when a problem occurs in any
signal, the estimated absolute vehicle speed and the signal are
mutually complemented.
[0195] As shown in FIG. 10, a lateral acceleration sensor 21, a
longitudinal acceleration sensor 22 and a yaw rate sensor 38 are
arranged in the vicinity of the center of gravity.
[0196] Besides, differentiating circuits 23, 24 that differentiate
the output of the respective acceleration sensors and acquire jerk
information are mounted.
[0197] Further, a differentiating circuit 25 for differentiating
the output of the yaw rate sensor 38 and acquiring a yaw angle
acceleration signal is mounted.
[0198] In this embodiment, to clarify the existence of the
differentiating circuits, the differentiating circuits seem to be
installed in each sensor, however, actually, an acceleration signal
is directly input to the central controller 40 and after various
operations, processing for differentiation may be also executed.
Processing for differentiation may be also executed in the central
controller 40 using a yaw rate estimated in the vehicle speed
sensor so as to acquire yaw acceleration of the vehicle body.
[0199] Besides, a differentiating circuit is included in an MEMS
type acceleration sensor unit that recently makes remarkable
progress and a sensor that outputs a jerk acquired by directly
differentiating a signal proportional to acceleration from a
sensing element may be also used. A signal output from the
acceleration sensor is often a signal that passes a low pass filter
for smoothing a signal.
[0200] To acquire a jerk, a precise jerk signal hardly having a
phase lag can be acquired differently from a signal which passes
the low pass filter once and which is differentiated again.
[0201] Besides, a jerk sensor that can directly sense a jerk and is
disclosed in Japanese Unexamined Patent Application Publication No.
2002-340925 may be also used.
[0202] The longitudinal acceleration sensor, the lateral
acceleration sensor, the yaw rate sensor, the differentiating
circuit and others seem to be clearly independent in the drawing,
however, longitudinal/lateral acceleration, a jerk, a yaw rate and
yaw acceleration may be directly output from a combined sensor 200
in which these performance is housed in one case. Further, a
function that calculates and outputs an acceleration command value
linked with a lateral motion shown in the mathematical expression 1
may be also integrated with the combined sensor.
[0203] This command value is superimposed on a CAN signal, the
signal is transmitted to a brake unit or the drive unit, and
G-Vectoring control may be also made.
[0204] In such configuration, the G-Vectoring control can be
realized using the existing brake unit and the existing drive unit
by only mounting the combined sensor in the vehicle.
[0205] Besides, in this embodiment, a method of estimating lateral
acceleration G.sub.y and a lateral jerk G.sub.y.sub.--.sub.dot is
also adopted. An estimate is made based upon a steering angle and
vehicle speed or based upon a yaw rate sensed by the yaw rate
sensor and vehicle speed.
[0206] Referring to FIG. 11, the method of estimating a lateral
acceleration estimate G.sub.ye and a lateral jerk estimate
G.sub.ye.sub.--.sub.dot based upon a steering angle 8 will be
described below.
[0207] First, in a vehicular lateral motion model, a yaw rate r in
steady circular turning from which a dynamic characteristic is
omitted will be calculated in the following mathematical expression
2 using a steering angle 6 [deg] and vehicular speed V [m/s] for
input.
[ Mathematical expression 2 ] r = 1 1 + AV 2 V 1 .delta. (
Mathematical expression 2 ) ##EQU00002##
[0208] In this expression, a stability factor A and a wheel base l
are a parameter proper to a vehicle and are a value acquired in an
experiment.
[0209] Besides, the lateral acceleration G.sub.y of the vehicle can
be acquired in the following mathematical expression 3 using
vehicular speed V, vehicular slip angle varying speed
.beta..sub.--dot and a yaw rate r.
[Mathematical expression 3]
G.sub.y=V({dot over (.beta.)}+r).apprxeq.Vr (Mathematical
expression 3)
[0210] .beta..sub.--dot is a motion in a linear range of tire force
and is quantity which can be omitted because it is small.
[0211] As described above, lateral acceleration
G.sub.ye.sub.--.sub.wod is calculated by multiplying the yaw rate r
from which the dynamic characteristic is omitted and vehicle speed
V. This lateral acceleration does not include the dynamic
characteristic of the vehicle having a characteristic of a response
lag in a low-frequency band.
[0212] This reason is as follows. To acquire vehicular lateral jerk
information G.sub.y.sub.--.sub.dot, lateral acceleration G.sub.y is
required to be differentiated in discrete time, that is, time
differentiation processing is required to be applied to lateral
acceleration measured by the lateral acceleration sensor. At this
time, a noise component of a signal is increased. To use this
signal for control, the signal is required to pass a low pass
filter (LPF), however, this causes a phase lag. Then, a method of
calculating acceleration in an earlier phase from which the dynamic
characteristic is omitted than proper acceleration and making the
calculated acceleration pass the LPF in a time constant T.sub.1pfe
after discrete differentiation is adopted so as to acquire a
jerk.
[0213] This may be also considered to be it that a dynamic
characteristic of lateral acceleration is represented by a lag by
the LPF and acquired acceleration is merely differentiated. Lateral
acceleration G.sub.y is also made to pass the LPF in the same time
constant T.sub.1pf. As a result, the dynamic characteristic is
applied to the acceleration and though the drawing is omitted, it
is verified that an actual acceleration response can be represented
well in a linear range.
[0214] As described above, the method of calculating lateral
acceleration G.sub.y and a lateral jerk G.sub.y.sub.--.sub.dot
using a steering angle has an advantage that the effect of noise is
inhibited and a response lag of the lateral acceleration G.sub.r
and the lateral jerk G.sub.y.sub.--.sub.dot is reduced.
[0215] However, in this estimate method, as skid information of the
vehicle is omitted and a nonlinear characteristic of the tire is
ignored, the actual lateral acceleration of the vehicle is required
to be measured and utilized when a slip angle increases.
[0216] FIG. 12 shows a method of acquiring lateral acceleration
G.sub.ys for control and jerk information G.sub.ys.sub.--.sub.dot
using a signal G.sub.yeo sensed by an MEMS element 210 in the
combined sensor 200 for example. As noise components such as
irregularities of road surfaces are included, the signal sensed by
the element is also required to pass a low pass filter (a time
constant T.sub.1pfs) (not dynamic compensation).
[0217] In the combined sensor 200, a G-Vectoring control command is
operated based upon the mathematical expression 1 in an
acceleration/deceleration command arithmetic unit 1200 using
acquired lateral acceleration G.sub.ys for control and lateral jerk
information G.sub.ys.sub.--.sub.dot and an
acceleration/deceleration command value G.sub.xt may be also
output.
[0218] To make respective merits of the estimate and the
measurement of lateral acceleration and a jerk compatible, in this
embodiment, a method of complementarily using both signals as shown
in FIG. 13 is adopted.
[0219] An estimated signal (a subscript of e is added) and a sensed
signal (a subscript of s is added) are added by multiplying by gain
made variable based upon skid information including a slip angle
.beta. and a yaw rate r.
[0220] Variable gain K.sub.je (K.sub.je<1) for a lateral jerk
estimated signal G.sub.ye is varied so that it has a great value in
a region in which a slip angle is small and has a small value when
a skid increases. Besides, variable gain K.sub.js (K.sub.js<1)
for a lateral jerk sensed signal G.sub.ys.sub.--.sub.dot is varied
so that it has a small value in the region in which a slip angle is
small and has a great value when a skid increases.
[0221] Similarly, variable gain K.sub.ge (K.sub.ge<1) for a
lateral acceleration estimated value G.sub.ye is varied so that it
has a great value in the region in which a slip angle is small and
has a small value when a skid increases. Besides, variable gain
K.sub.gs (K.sub.gs<1) for a lateral acceleration sensed signal
G.sub.ys is varied so that it has a small value in the region in
which a slip angle is small and has a great value when a skid
increases.
[0222] Such configuration enables small noise from a normal region
in which a slip angle is small to a critical region in which a skid
grows and acquiring an acceleration signal and a jerk signal
respectively suitable for control. These gain is determined by a
function of skid information or a map.
[0223] The configuration of the system in the first embodiment of
the vehicular motion control system according to the present
invention and the method of estimating lateral acceleration and a
lateral jerk (these may be also included in the combined sensor 200
in which the sensors in FIG. 10 are integrated or as a logic in the
central controller 40) have been described.
[0224] Next, system configuration including the logic according to
the present invention will be described referring to FIG. 14. In
this embodiment, the system configuration is control configuration
in which acceleration/deceleration control by G-Vectoring described
in a nonpatent literature 6 (Takahashi, Yamakado, Saito, Yokoyama:
Actual vehicle performance evaluation of skid prevention system
using the G-Vectoring control for understeer control, collection of
Society of Automotive Engineers of Japan Vol. 41, No. 2, pp
195-200, 2010) and yaw moment control by vehicular skid prevention
control (DYC) are fused.
[0225] FIG. 14 schematically shows relation among an operation
control logic of the central controller 40 which is a control
means, the vehicle 0 and an observer that estimates a slip angle
based upon the group of sensors and a signal from the sensor
(though the signal is operated in the central controller 40). The
whole logic is roughly configured by a vehicular motion model 401,
a G-Vectoring controller 402, a yaw moment controller 403 and a
braking force/driving force distributor 404.
[0226] That is, the central controller 40 which is the control
means generates an acceleration/deceleration command based upon a
sensed steering angle .delta. and sensed vehicle speed V. It is an
acceleration/deceleration command generating means (the vehicular
motion model 401, the G-Vectoring controller 402 and the yaw moment
controller 403) that generates the acceleration/deceleration
command. Concretely, the acceleration/deceleration command includes
target longitudinal acceleration and the target yaw moment
respectively generated based upon a steering angle and vehicle
speed. Besides, in the braking force/driving force distributor 404
which is a driving force/braking force distribution means, the
distribution of the driving force or the driving torque of each
wheel and/or braking force or braking torque is determined.
[0227] The vehicular motion model 401 estimates estimated lateral
acceleration (G.sub.ye), a target yaw rate r.sub.t and a target
slip angle .beta..sub.t based upon a steering angle .delta. input
from the driver steered angle sensor 33 and vehicle speed V using
the mathematical expressions 2, 3. In this embodiment, the target
yaw rate r.sub.t is set to the same as the yaw rate r.sub..delta.
acquired based upon steering described above.
[0228] As for lateral acceleration and a lateral jerk respectively
input to the G-Vectoring controller 402, a signal processing unit
(a logic) 410 that complementarily uses both signals as shown in
FIG. 4 is adopted.
[0229] The G-Vectoring controller 402 determines a component linked
with a current vehicular lateral motion in a target longitudinal
acceleration command G.sub.Xt using these lateral acceleration and
lateral jerk according to the mathematical expression 1. Further,
G.sub.x.sub.--.sub.DC which is a deceleration component not linked
with the current vehicular lateral motion is added, the target
longitudinal acceleration command G.sub.Xt is calculated, and the
target longitudinal acceleration command is output to the braking
force/driving force distributor 404. That is, the target
longitudinal acceleration command G.sub.Xt is calculated based upon
estimated lateral acceleration calculated based upon a steering
angle and vehicle speed and a lateral jerk calculated based upon
the estimated lateral acceleration.
[0230] In this case, G.sub.x.sub.--.sub.DC is an item required for
foreseen deceleration when a corner exists in front or when an
interval speed command is issued. As the interval speed command is
information determined based upon coordinates on which the driver's
vehicle exists, it can be determined by collating coordinate data
acquired by GPS and others with map information in which the
interval speed command is included.
[0231] Next, though the details of sensing are omitted in this
embodiment, foreseen deceleration for a corner in front can be
realized by a method of taking information in front of the driver's
vehicle such as obstacle information, preceding vehicle information
and following vehicle information depending upon a camera such as a
single-lens camera and a stereoscopic camera, a laser, a distance
measuring radar in units of a millimeter wave and others or GPS
information and others as an external information sensing means and
accelerating/decelerating according to a future lateral motion (a
future lateral jerk) not actual at the present time. In this case,
control that an acceleration/deceleration command is turned zero by
external field information including any of obstacle information,
preceding vehicle information and following vehicle information
respectively sensed by the external information sensing means can
be also made.
[0232] A future steering angle is estimated as in a so-called
driver model in which a steering angle is determined using a path
in forward watch distance/time and deviation information in the
driver's vehicle reach estimated position. Foreseen deceleration
for a corner in front is enabled by performing G-Vectoring as in
the mathematical expression 1 according to a future lateral jerk to
be generated in the vehicle by steering operation (preview
G-Vectoring).
[0233] Next, the target yaw moment M.sub.t is calculated based upon
deviation .DELTA.r between a target yaw rate r.sub.t
(r.sub..delta.) and a target slip angle .beta..sub.t and deviation
.DELTA..beta. between a real yaw rate and a real (estimated) slip
angle in the yaw moment controller 403 and is output to a braking
force/driving force distributor 404. The target yaw moment M.sub.t
is calculated based upon a steering angle, vehicle speed, a yaw
rate and a slip angle of the vehicle.
[0234] The braking force/driving force distributor 404 first
determines initial basic braking force/driving force
(F.sub.xfl.sub.--.sub.o, F.sub.xfr.sub.--.sub.o,
F.sub.xrl.sub.--.sub.o, F.sub.xrr.sub.--.sub.o) of the four wheels
of the vehicle 0 based upon a target longitudinal acceleration
command G.sub.xt which is an acceleration/deceleration command and
the target yaw moment M.sub.t. The braking force/driving force
distributor has such configuration that the basic braking
force/driving force is distributed according to the distribution of
braking force/driving force (hereinafter called diagonal
distribution) according to the present invention based upon a
turning direction sensed based upon at least any of an input
steering angle, an input vehicular yaw rate and input vehicular
lateral acceleration.
[0235] In the distribution of braking force/driving force
(hereinafter called diagonal distribution) according to the present
invention, as it is determined that for the front wheels, more
driving force/driving torque and/or more braking force/braking
torque are/is distributed to the inside front wheel in turning than
that to the outside front wheel in turning and for the rear wheels,
more driving force/driving torque and/or more braking force/braking
torque are/is distributed to the outside rear wheel in turning than
that to the inside rear wheel in turning, a normal load on the side
of the inside wheel decreases because of the transfer of a load
from the inside wheel in turning to the outside wheel in turning
when lateral acceleration increases, longitudinal force decreases
because of the increase of slip ratio, and lateral force also
decreases.
[0236] In such a situation, the diagonal distribution is not
effective any longer and is required to be returned to the basic
braking force/driving force of the four wheels described above (a
degree of the diagonal distribution is gradually decreased). In
view of such a background, the basic braking force/driving force is
first calculated. First, an initial basic distribution rule will be
described and afterward, the details of the diagonal distribution
will be described.
[0237] Referring to FIG. 15, equations of a longitudinal motion, a
lateral motion and a yawing motion will be considered. To make the
equations clearly understandable, braking force/driving force and
tire lateral force for the two wheels will be redefined as
follows.
[Mathematical expression 4]
F.sub.xr.sub.--.sub.o=F.sub.xfr.sub.--.sub.o+F.sub.xrr.sub.--.sub.o
(Mathematical expression 4)
[Mathematical expression 5]
F.sub.xl.sub.--.sub.o=F.sub.xfl.sub.--.sub.o+F.sub.xrl.sub.--.sub.o
(Mathematical expression 5)
[Mathematical expression 6]
F.sub.yf=F.sub.yfl+F.sub.yfr (Mathematical expression 6)
[Mathematical expression 7]
F.sub.yr=F.sub.yrl+F.sub.yrr (Mathematical expression 7)
[0238] When the above-mentioned force for the two wheels is
redefined as described above, various motions will be expressed as
follows.
<Longitudinal Motion>
[0239] [Mathematical expression 8]
mG.sub.xt=F.sub.xl.sub.--.sub.o+F.sub.xr.sub.--.sub.o (Mathematical
expression 8)
<Lateral Motion>
[0240] [Mathematical expression 9]
mG.sub.y=F.sub.yF+F.sub.yr (Mathematical expression 9)
<Yawing Motion>
[0241] [ Mathematical expression 10 ] I z r . = ( l f F yf - l r F
yr ) + d 2 ( F xr_o - F xl_o ) ( Mathematical expression 10 )
##EQU00003##
[0242] Further, the target yawing moment and braking force/driving
force to each wheel will be expressed as follows.
[ Mathematical expression 11 ] M t = d 2 ( F xr_o - F xl_o ) (
Mathematical expression 11 ) ##EQU00004##
When the longitudinal motion (mathematical expression 8) and the
yawing moment (mathematical expression 11) are apposed, they can be
analytically settled with two unknown letters and two expressions
as follows.
[ Mathematical expression 12 ] F xl_o = m 2 G xt + M t d (
Mathematical expression 12 ) [ Mathematical expression 13 ] F xr_o
= m 2 G xt - M t d ( Mathematical expression 13 ) ##EQU00005##
[0243] As a result, braking force/driving force for the two front
and rear wheels on the right side and braking force/driving force
for the two front and rear wheels on the left side where an
acceleration/deceleration command by the G-Vectoring control and a
moment command by skid prevention control are made compatible can
be distributed.
[0244] Next, these are distributed to the front and rear wheels
according to the ratio in a normal load of the front and rear
wheels. When the height from the ground of the sprung center of
gravity of the vehicle 0 is h and the vehicle 0 is
accelerated/decelerated at G.sub.xt, loads (W.sub.f, W.sub.r) for
the two front and rear wheels are as follows.
[ Mathematical expression 14 ] W f = mgl r - mhG xt 1 (
Mathematical expression 14 ) [ Mathematical expression 15 ] W r =
mgl f + mhG xt 1 ( Mathematical expression 15 ) ##EQU00006##
[0245] Therefore, the braking force/driving force of the four
wheels distributed according to the ratio of loads are as
follows.
[ Mathematical expression 16 ] F xf l _o = g l r - hG xt g l ( m 2
G xt + M t d ) ( Mathematical expression 16 ) [ Mathematical
expression 17 ] F xfr_o = g l r - hG xt g l ( m 2 G xt - M t d ) (
Mathematical expression 17 ) [ Mathematical expression 18 ] F xr 1
_o = g l f + hG xt g l ( m 2 G xt + M t d ) ( Mathematical
expression 18 ) [ Mathematical expression 19 ] F xrr_o = g l f + hG
xt g l ( m 2 G xt - M t d ) ( Mathematical expression 19 )
##EQU00007##
[0246] However, as follows.
[ Mathematical expression 20 ] G xt = - sgn ( G y G . y ) C xy 1 +
T s G . y + G x_DC ( Mathematical expression 20 ) [ Mathematical
expression 21 ] M t = M ( r .delta. rG y r s .beta. t .beta. s ) (
Mathematical expression 21 ) ##EQU00008##
[0247] The details of the mathematical expression 21 are calculated
using the similar method to a method disclosed in Japanese
Unexamined Patent Application Publication No. 1997-315277.
[0248] The initial basic distribution rule has been described. When
the mathematical expression 19 is viewed in view of the
mathematical expression 16, it can be said that a yaw moment
command by slid prevention control is distributed according to a
static load of the front and rear wheels while a G-Vectoring
control command value G.sub.xt is zero and braking force/driving
force for realizing longitudinal acceleration and/is distributed
longitudinally according to weight distribution ratio with the same
value applied to the right and left wheels so as to prevent extra
moment from being caused while a G-Vectoring control command value
G.sub.xt is not zero.
[0249] Next, a concrete method of diagonally distributing initial
basic braking force/driving force determined in the mathematical
expression 19 based upon the mathematical expression 16 will be
described referring to FIG. 16.
[0250] First, the sum of the front wheels F.sub.xfl.sub.--.sub.o
and F.sub.xfr.sub.--.sub.o and the sum of the rear wheels
F.sub.xrl.sub.--.sub.o and F.sub.xrr.sub.--.sub.o in initial basic
distribution are calculated. Braking force/driving force
(F.sub.xf1, F.sub.xfr, F.sub.xrl, F.sub.xrr) to each wheel and/is
determined by multiplying the sum by gain of (1+.alpha.)/2 as to
the left front wheel, multiplying the sum by gain of (1-.alpha.)/2
as to the right front wheel, multiplying the sum by gain of
(1-.alpha.)/2 as to the left rear wheel and multiplying the sum by
gain of (1+.alpha.)/2 as to the right rear wheel.
[0251] A lateral distribution index .alpha. will be described
below. .alpha. can have values between +1 and -1. A situation in
which a has a characteristic value will be described to acquire
intuitional understanding below:
(1) When .alpha.=0, the same braking force/driving force is caused
in the front wheels or the rear wheels. (2) When .alpha.=1, braking
force/driving force is caused only in the left front wheel and the
right rear wheel. (3) When .alpha.=-1, braking force/driving force
is caused only in the right front wheel and the left rear
wheel.
[0252] As clear from the above-mentioned, when a is positive,
control is made in leftward turning so that more braking
force/driving force is caused in the inside front wheel in turning
and the outside rear wheel in turning and at this time, the
operability and stability are enhanced. Conversely, when .alpha. is
negative, control is made in rightward turning so that more braking
force/driving force is caused in the inside front wheel in turning
and the outside rear wheel in turning and at this time, the
operability and stability are enhanced.
[0253] In leftward turning, a steering angle, a yaw rate and
lateral acceleration G.sub.y have positive values (a standard by
JASO that the z-axis is positive upward is adopted). Therefore, as
shown in FIG. 16, in a graph having acceleration on an abscissa for
example, when lateral acceleration G.sub.y is positive, .alpha. has
only to be set to have a positive value (<1) and when lateral
acceleration G.sub.y is negative, .alpha. has only to be set to
have a negative value (>-1). In place of lateral acceleration
G.sub.y, .alpha. may be also determined based upon whether a
steering angle .delta. and a yaw rate r are positive or not.
[0254] To determine .alpha., operation (.alpha..noteq.0) or
nonoperation (.alpha.=0) may be also selected a moment command Mzt.
As Mzt is calculated based upon slid information of the vehicle,
Mzt is issued when skid occurs in the vehicle and stability is
deteriorated.
[0255] In diagonal distribution control according to the present
invention, as braking force/braking torque and/or driving
force/driving torque are/is distributed to the inside wheel and the
outside wheel of the vehicle, moment is basically not directly
applied to the vehicle.
[0256] However, generally, it is considered that when skid
prevention control is operated, the vehicle is in an unstable
condition. Accordingly, for safety, in a situation that yaw moment
control is operated based upon the mathematical expression 21, the
diagonal distribution control is stopped, that is, .alpha. may be
also set to 0. That is, when a skid prevention function is
operated, control over the distribution of driving force/driving
torque and/or braking force/braking torque to each wheel may be
also stopped.
[0257] Besides, when lateral acceleration G.sub.y increases, a load
inside turning remarkably decreases because of the balance of the
moment by inertia force, the slip ratio of the inside front wheel
rapidly rises in the diagonal distribution, the cornering force of
the front wheel also decreases far from being unable to realize
deceleration, and the front of the vehicle slips.
[0258] In the graph (the map) in which relation with lateral
acceleration G.sub.y-.alpha. shown in FIG. 16 is determined, when
an absolute value of lateral acceleration G.sub.y grows, a value of
.alpha. is made to approximate zero and control is made so that the
diagonal distribution is made to approximate basic distribution in
which braking force/driving force is equally distributed to the
right and left wheels. Besides, even if longitudinal acceleration
G.sub.x or a product of longitudinal acceleration G.sub.x and
lateral acceleration G.sub.y is used so as to adjust so that
.alpha. similarly decreases, the similar or more effect is
acquired.
[0259] Further, as shown in FIGS. 8C and 9C, when such control over
braking force and driving force that braking force is applied to
the inside front wheel and driving force is applied to the outside
front wheel is simultaneously made, the control can be facilitated
by doubling a value of .alpha. at the maximum.
[0260] For example, when .alpha.=2, control is made so that
deceleration of 1.5 times for twice in basic distribution is
produced in the inside front wheel and braking force of -0.5 times,
that is, driving force for twice in the basic distribution is
produced in the outside front wheel. Hereby, braking force can be
produced in the inside front wheel and driving force can be
produced in the outside front wheel, producing the same braking
force in lateral total as that in the basic distribution (for the
rear wheels, also similar).
[0261] A motion of the vehicle when the diagonal distribution
control according to the present invention is applied will be
described on the supposition of concrete running below.
[0262] A supposed scene is similar to the scene shown in FIG. 6. A
general running scene including approach and escape to/from a
corner in which a direct advance route A, a transient interval B, a
steady turning interval C, a transient interval D and a direct
advance interval E are included is supposed. At this time, no
acceleration/deceleration operation by a driver shall be made.
[0263] FIG. 17 shows a steering angle, lateral acceleration, a
lateral jerk, an acceleration/deceleration command calculated in
the mathematical expression 1 and the results of diagonally
distributing force for braking and driving the four wheels as
waveforms in a time history.
[0264] As described above, more driving force/braking force is
distributed to the inside front wheel and the outside rear wheel
and less driving force/braking force is distributed to the outside
front wheel and the inside rear wheel.
[0265] FIG. 18(a) to FIG. 18(e) show a situation in which braking
force/driving force at this time and the compliance steer of the
front and rear wheels are generated every point time (1 to 7) shown
on the upside of FIG. 17.
[0266] As described above, when the G-Vectoring control is applied
to the vehicle, an acceleration/deceleration motion linked with a
lateral motion can be realized if only a driver steers for
turning.
[0267] Besides, the similar control to four-wheel active steer is
enabled by diagonally distributing braking force and driving force
for realizing acceleration/deceleration (by distributing more
driving force/braking force to the inside front wheel and the
outside rear wheel).
[0268] In addition, as acceleration/deceleration basically realized
by the G-Vectoring control is also realized in a condition of the
diagonal distribution, this motion is a characteristic motion
having smooth curved transition as shown on the downside of FIG. 6
when this motion is expressed in a "g-g" diagram having
longitudinal acceleration on an axis of abscissas, having lateral
acceleration on an axis of ordinates and showing a mode of
acceleration caused in the vehicle.
[0269] This curved transition shows clockwise transition at a left
corner as shown on the downside of FIG. 6, shows transition
inverted on an axis of G.sub.x at a right corner, and a direction
of the transition is counterclockwise. In such transition, a
pitching motion caused in the vehicle by longitudinal acceleration
and a roll motion caused by lateral acceleration are suitably
linked and peak values of a roll rate and a pitching rate are
reduced.
[0270] FIG. 19 and FIGS. 20 (a) to 20 (e) show a situation in which
the diagonal distribution control according to the present
invention that braking force/driving force are simultaneously
generated is applied in addition to the diagonal distribution. A
supposed scene is similar to those in FIG. 6, FIG. 17 and FIGS. 18
(a) to 18(e).
[0271] An acceleration/deceleration command by the G-Vectoring
control is realized, simultaneously controlling braking force and
driving force. Compared with FIGS. 17 and 18, effect closer to
four-wheel active steer is acquired.
[0272] Further, FIGS. 21 and 22 show not only automatic
acceleration/deceleration control by the G-Vectoring control but
results of a case that braking force and driving force are
individually distributed (FIG. 21) and a case that they are
simultaneously distributed (FIG. 22) respectively according to
braking operation and acceleration operation by a driver.
[0273] A turning direction is also sensed based upon a steering
angle, a yaw rate or lateral acceleration for the input of
acceleration/deceleration from a driver, for the front wheels, more
driving force/driving torque and more braking force/braking torque
can be distributed to the inside wheel in turning, and for the rear
wheels, more driving force/driving torque and more braking
force/braking torque can be distributed to the outside wheel in
turning. An acceleration command is turned zero when a braking
operation command from a driver is input and a deceleration command
is turned zero when an accelerating operation command from the
driver is input.
[0274] Similarly, the distribution rule described in the present
invention can be also applied to acceleration/deceleration control
linked with a lateral motion based upon a control rule except
G-Vectoring.
[0275] Next, a result of applying the present invention to full
vehicle simulation will be described.
[0276] FIG. 23 shows a simulation model. Each wheel is modeled as
shown in FIG. 23 so that compliance steer is caused by longitudinal
force or lateral force. A compliance value is set to a consistent
value such as 0.5.degree. outside to 0.5.degree. inside/980 N
(braking force/driving force) according to the nonpatent literature
5, 0 to 0.2.degree. outside/980 N as to the front wheel and -0.1 to
0.1 inside/980 N as to the rear wheel (compliance steer by lateral
force is also considered). As for a tire model, force in a
longitudinal direction and force in a lateral direction can be
simultaneously considered.
[0277] In the simulation, a brushed tire model adjusted based upon
experimental data is used.
[0278] Though a concrete equation of motion is omitted, numerical
calculation is made based upon the similar equation to an equation
(p. 11: Expression (2.1.24-1) to (2.1.24-6) described in Chap. 2,
"Motion equation of automobile and its linearization" of a
nonpatent literature 7 (H. Harada: Vehicle dynamics for automotive
engineers, Industrial science systems, pp. 8-11, pp. 152-153,
2005).
[0279] FIGS. 24A to 24C show results of calculation in which the
similar situation that turning is started from a line and is
escaped after steady turning to FIG. 6 is simulated. As they are
the results of calculation based upon input of a steering angle, an
effect that a steering angle is turned from the side of the tire
(compliance with an arm of a driver) is not considered.
[0280] FIG. 24(a) shows a case of no acceleration/deceleration
control linked with a lateral motion, FIG. 24 (b) shows a case of
only the G-Vectoring control, and FIG. 24(c) shows a result of the
calculation of a steering angle according to the present invention
in which G-Vectoring and the diagonal distribution are combined
(the steering angle is shown in the shape of an angle of the
tire).
[0281] In the calculation shown in FIG. 24C according to the
present invention, to clarify the effect, distribution to the
outside front wheel and the inside rear wheel is set to zero (that
is, a case of .alpha.=0 in FIG. 16).
[0282] Besides, a drawing in which an orientation of each wheel is
schematically shown is also shown in the result of each
calculation. As compliance steer by lateral force (in a direction
of toe-out) is added and especially in escape of turning, only
lower acceleration (lower driving force), compared with
deceleration can be realized, the variation by control of a
steering angle is not great so much. Nevertheless, it is known in
view of time when turning is started and time when turning is
escaped in FIG. 24 that the control of compliance steer by the
diagonal distribution of braking force/driving force according to
the present invention which has been described can be realized. It
is known that especially, a steering angle of the front wheel
increases at the beginning of turning (to an extent that toe-out is
corrected by braking force equally distributed to the front wheels
by the G-Vectoring control).
[0283] Further, FIG. 25 shows a result of calculation in which a
locus at this time of the vehicle is compared. As the interval of
steady turning (the point time 3 to 5 shown on the upside of FIG.
17) is short, the steady turning is not in the shape of a U-turn.
In spite of the same steering angle (viewed from a driver), it is
known that the vehicle is turned inside in the case of only the
G-Vectoring control, compared with the case of no control and the
vehicle is turned more inside in the case of control according to
the present invention.
[0284] The inventors execute driving simulator experiments and
verify that in a situation in which a driver enters a blind corner
and the blind corner has a sharp curve, he/she cannot tread a brake
pedal promptly though he/she more turns the steering wheel. In such
a situation, when the G-Vectoring control and further, the present
invention are applied, it can be expected that deviation from a
road can be also avoided and safety is greatly enhanced.
[0285] The above description of the first embodiment related to the
vehicle 0 in which braking force/driving force can be freely
controlled every wheel is finished.
[0286] Next, the configuration of a vehicle equivalent to a second
embodiment in which the present invention is applied to a normal
vehicle where four wheels are independent and only deceleration
torque can be controlled will be described and a result of
experiment actually using the vehicle will be described.
Second Embodiment
[0287] FIG. 26 shows the whole configuration of a second embodiment
of the vehicular motion control system according to the present
invention.
[0288] In a vehicle 2010 in this embodiment, front wheels are
driven by an engine 2001. A braking device 2460 is a hydraulic
brake and is provided with a brake pedal 2461, an electric servo
unit 2462, a primary piston 2464, and a secondary piston 2465.
[0289] A hydraulic oil piping is a general so-called X piping
(diagonal piping), normally, a brake caliper 2071 for a left front
wheel 2061 and a brake caliper 2074 for a right rear wheel 2064
communicate via a hydraulic oil piping 2454, and a brake caliper
2072 for a right front wheel 2062 and a brake caliper 2073 for a
left rear wheel 2063 communicate via a hydraulic oil piping 2455
(basically, the hydraulic oil piping 2454 is pressurized by the
primary piston 2464 and the hydraulic oil piping 2455 is
pressurized by the secondary piston 2464).
[0290] Further, a skid prevention device 2450 is provided and can
independently control the driving force and/or the braking force of
each of the four wheels based upon skid information (a slip angle
.beta. and a yaw rate r) calculated based upon a steering angle and
vehicle speed or sensed.
[0291] For a sensor, a combined sensor 2200 manufactured by MEMS
that can sense longitudinal acceleration, lateral acceleration and
a yaw rate is mounted. The sensor may be also mounted in the
vicinity of the center of gravity of the vehicle or in the skid
prevention device so as to enable sensing longitudinal acceleration
and lateral acceleration respectively by coordinate transformation
in the center of gravity of the vehicle (a yaw rate is
substantially the same). The combined sensor 2200 is provided with
an arithmetic circuit such as a differentiating circuit, a lateral
jerk is acquired by differentiating information proportional to
lateral acceleration output from a sensing element, a G-Vectoring
control command is calculated in a mathematical expression 1, and
is output to the skid prevention device 2450.
[0292] The skid prevention device 2450 which is a control means is
provided with an oil pressure generator 2451 that drives a gear
pump of a seal block type by a motor, a group of oil pressure
proportional/on-off valves 2452 and a controller 2453, and controls
pressure in the hydraulic oil piping 2454 and pressure in the
hydraulic oil piping 2455.
[0293] In this configuration, when a skid prevention function is
operated, a diagonal distribution function according to the present
invention is stopped though the details of its logic are described
above. Besides, this configuration is such configuration that
control is stopped when a back gear is put in a view of a gear
position of a transmission, control is stopped.
[0294] A diameter of the piston that presses a brake pad of the
front/rear wheel and an effective radius from an axle to the center
of the pad are different between the front wheel and the rear wheel
and they are designed to approach braking force ideal distribution
in consideration of the transfer of a load (refer to a nonpatent
literature 7: Chap. 7, Braking performance and driving performance,
7.2 Distribution of braking force, pp. 152-153).
[0295] In the present invention, in leftward turning, great braking
force is required to be generated in the left front wheel 2061
which is the inside front wheel and the left rear wheel 2064 which
is the outside rear wheel. The hydraulic brake and the X piping in
this embodiment have the following degree of freedom in selection
in the configuration.
(1) Same Pressure Distribution
[0296] As the brake caliper 2071 for the left front wheel 2061 and
the brake caliper 2074 for the right rear wheel 2064 communicate
via the hydraulic oil piping 2454, the skid prevention device 2450
which is the control means controls pressure in the hydraulic oil
piping 2454 and pressure in the hydraulic oil piping 2455 at
distribution ratio .alpha. shown in FIG. 16. That is, the skid
prevention device 2450 controls so that internal pressure in the
hydraulic oil piping 2454 that communicates with the inside front
wheel in turning and the outside rear wheel in turning or the
hydraulic oil piping 2455 is substantially the same. Hereby, in
longitudinal distribution, the same pressure distribution has a
merit that an initial design value of the braking device can be
followed and no complex control valve is required.
[0297] In the meantime, as braking force is distributed in
consideration of the transfer of a load in deceleration in control
under the same pressure, braking force in the front wheel is
greater than that in the rear wheel slightly floating. At such
time, as difference is made between braking force in the front
wheels and braking force in the rear wheels, the moment acquired by
multiplying each braking force by a value of a half of a tread
(distance between the right and left wheels) is generated. To
cancel the moment, there are the following methods.
(2) Same Braking Torque Distribution
[0298] The ratio in a diameter of each piston of the front and rear
wheels, distance from the center and others are calculated back and
hydraulic distribution is varied in a longitudinal direction to be
the same braking torque. That is, hydraulic distribution is varied
in the longitudinal direction so that the braking torque of the
inside front wheel in turning and the braking torque of the outside
rear wheel in turning are substantially equal. For example,
distribution is varied so that the oil pressure of the front wheel
is smaller and the oil pressure of the rear wheel is larger.
(3) Same Braking Force Distribution
[0299] In (2), when a load onto the wheel is different, actual
braking force is different. When a load of each wheel is estimated
based upon the first distribution of longitudinal weight, a wheel
base, tread, the height of the gravitational center, sensed
longitudinal acceleration and sensed lateral acceleration using
expressions on the upside of FIG. 27 and braking force is strictly
controlled based upon a map shown on the downside of FIG. 27
showing the estimated load and slip ratio of the wheel and others,
the above-mentioned moment can be completely canceled. That is,
distribution is made so that the braking force of the inside front
wheel in turning and the braking force of the outside rear wheel in
turning are substantially equal.
[0300] Generally, as the vehicle is designed to be understeer, the
moment produced by the same pressure distribution conversely
buffers understeer and has effect that turning is facilitated,
however, when control tries to correspond from neutral steer to
oversteer, the distribution of same braking torque and same braking
force is also required to be considered.
[0301] As described above, when the configuration is made so that
diagonal distribution control according to the present invention is
stopped while skid information such as the occurrence of oversteer
is generated and lateral acceleration, longitudinal acceleration or
the product of lateral acceleration and longitudinal acceleration
is large, the same pressure distribution described in (1) is
sufficiently practical.
[0302] The effects of the present invention will be described
below, showing results of experiments of a prototype vehicle in
which the distribution rule according to the present invention is
mounted.
[0303] First, FIG. 28 shows a result of measuring loci of the
center of gravity of the vehicle where rightward steady circular
turning is made at the radius of 40 m and at the speed of 60 km/h
on a vehicle speed meter and deceleration is made at 2 m/s.sup.2
(0.2 G) just on coordinates (0, 0) in a condition in which a
steering angle is fixed using differential global positioning
system (DGPS). It is known that when this distribution control is
executed, a degree of inside turning is stronger, compared with
deceleration in lateral equal distribution because of the toe-in of
the front wheel and the toe-out of the outside rear wheel described
above.
[0304] For a reference experiment for comparison, when reverse
distribution(distribution to the outside front wheel and the inside
rear wheel) is made, turning is greater outside than that in
lateral equal distribution and this indirectly proves that a basic
characteristic (the enhancement of steering gain) desired in the
present invention is realized as a reverse event.
[0305] This result shows that the enhancement of turning
performance can be expected not only in automatic
acceleration/deceleration under the G-Vectoring control but in
acceleration/deceleration by a driver.
[0306] Next, an experiment of an L-type turn shown in FIG. 29 is
made. This experiment is a task that a circular arc having the
radius of 40 m is traced from a line by 1/4, the orientation is
changed by 90 degrees and afterward, the turn is linearly escaped.
Pylons are set on both sides of a course, no transition curve
exists from 50 m on an X coordinate, and the circular arc having
the radius of 40 m is formed. This is a test in which a situation
that a curve of a blind corner proves to be sharp in the blind
corner is simulated.
[0307] FIG. 29 shows the comparison of a locus depending upon
lateral equal distribution by G-Vectoring and a locus (a vehicular
image is displayed every 0.5 sec) according to the present
invention (diagonal distribution (same pressure) is applied to
G-Vectoring). It can be verified that respective vehicles show the
substantial same locus.
[0308] FIG. 30 shows respective vehicle speed at this time. The
vehicle speed is adjusted so that it is 70 km/h on the meter at the
coordinates (0, 0). Afterward, an effect of engine brake is removed
with an automatic transmission neutral. A test that a driver did
not tread a brake pedal and the diagonal distribution was made or
no diagonal distribution was made according to an automatic braking
command by the G-Vectoring control was performed.
[0309] FIG. 31 shows the time history data of braking pressure in
the front wheel and the rear wheel. FIG. 31 shows that in cases of
only G-Vectoring, the same braking oil pressure is applied to the
right and left front wheels and the right and left rear wheels. In
the meantime, in the diagonal distribution according to the present
invention, it is known that pressure equivalent to substantial
twice of a case of only G-Vectoring is equally applied to the
inside front wheel and the outside rear wheel and hydraulic
distribution to the outside front wheel and the inside rear wheel
is zero.
[0310] FIG. 32 shows the time history data of longitudinal
acceleration and lateral acceleration of the vehicle at this time
and a "g-g" diagram showing having longitudinal acceleration on an
axis of an abscissa, having lateral acceleration on an axis of an
ordinate and showing the transition of the linkage of longitudinal
acceleration and lateral acceleration. It is judged that when
lateral acceleration increases (a lateral jerk is generated),
deceleration is made according to the mathematical expression
1.
[0311] Besides, the collation of a steering angle shown in FIG. 33
and deceleration tells that when a steering angle increases, the
vehicle is decelerated.
[0312] Deceleration in 4 seconds is caused because of drag of a
tire by turning. As shown in the "g-g" diagram, longitudinal
acceleration and lateral acceleration are determined so that they
have curved transition as time elapses. This time, control on the
side of acceleration is not made, however, it is verified that a
control command is set so that the lateral acceleration of the
vehicle decreases, the vehicle is accelerated to be a negative
lateral jerk and so that when a steering angle of the vehicle
decreases, the vehicle is accelerated.
[0313] FIG. 33 compares a steering angle in the present invention
(G-Vectoring+the diagonal distribution) and in only G-Vectoring.
Though the substantial same locus is drawn in FIG. 29 and FIG. 30
is based upon the substantial same speed, it is known in the
control according to the present invention, compared with control
by only G-Vectoring that a steering angle can be reduced.
[0314] A drawing on the downside of FIG. 33 shows a steering angle
and a yaw rate generated at that time to more clarify this. In this
case, the inclination of these curves can be substantially regarded
as yaw rate gain at each steering angle because speed is the same.
The drawing tells that in the present invention (G-Vectoring+the
diagonal distribution), gain increases, compared with G-Vectoring
(uniform distribution).
[0315] It is clarified by the above that in the present invention
(G-Vectoring+the diagonal distribution), yaw rate gain increases,
compared with G-vectoring (the uniform distribution) and a corner
is cleared at a smaller steering angle, and it can be verified that
operability is obviously enhanced.
[0316] Further, the sense of a driver that a vehicle is
satisfactorily turned as if the vehicle were twisted is reported.
FIG. 34 shows a roll rate and a pitch rate at this time on position
coordinates (note: there are minute irregularities immediately
before approach to an L-type turn and the pitch like an impulse is
caused). In approach to the L-type turn, a pitch rate in the
present invention (G-Vectoring+the diagonal distribution) slightly
grows and a roll rate obviously grows (experiments are made plural
times and this is already verified).
[0317] In the patent literature 3, a vehicular behavior control
device that can effectively inhibit uncomfortable roll behavior in
turning by reverse diagonal distribution (an outside front wheel in
turning and an inside rear wheel in turning) to the present
invention in a vehicle provided with a suspension on the front
wheel side according to anti-dive geometry and a suspension on the
rear wheel side according to anti-lift geometry is proposed. This
is a mechanism that as the anti-dive moment in braking separately
acts on the right and left front wheels and the anti-lift moment
separately acts on the right and left rear wheels, the lift of a
vehicle body is laterally unbalanced and the moment that inhibits a
roll is generated. It is considered that in the diagonal
distribution according to the present invention (G-Vectoring+the
diagonal distribution), the moment reverse to this acts and a roll
rate grows.
[0318] FIG. 35 shows longitudinal acceleration, lateral
acceleration and a roll rate when braking force is diagonally
distributed to the left front wheel and the right rear wheel so
that the deceleration of -2 m/s.sup.2 is generated from a condition
of a direct advance. A steering angle is adjusted to possibly
prevent lateral acceleration by braking force applied to the front
wheel on one side from being caused.
[0319] FIG. 35 tells that a roll rate is also caused without the
roll moment by lateral acceleration and the above-mentioned
mechanism can be verified (anti-dive geometry is adopted for the
front wheel of this experimental vehicle). As described above, a
roll of the vehicle may increase according to the diagonal
distribution control according to the present invention.
Accordingly, a roll rate can be also controlled at the same
deceleration and at the same lateral acceleration by switching the
diagonal distribution and lateral equal distribution and a unified
sense of a pitch rate and a roll rate by acceleration/deceleration
can be adjusted. This can be considered to be direct roll-moment
control (DRC) in which the roll moment is directly adjusted.
[0320] Further, a results of an experiment related to the increase
of slips when the inside front wheel is braked by the lateral
transfer of a load described above will be described below and a
reason for switching the diagonal distribution to the lateral equal
distribution based upon lateral acceleration, longitudinal
acceleration or the product of lateral acceleration and
longitudinal acceleration will be described below.
[0321] FIG. 36 and the following show results of experiments in
running at 70 km/h on the meter on the same L-type turn course. In
both the present invention (G-Vectoring+the diagonal distribution)
and G-vectoring (uniform distribution), the course is cleared,
however, it can be verified in an enlarged view that a locus
according to the present invention is located outside. It is known
from FIG. 37 that speed at this time is slightly higher in the
present invention.
[0322] FIG. 38 shows time history data of braking pressure of the
front wheel and the rear wheel. It is known that in a case of only
G-Vectoring, the same braking oil pressure of approximately 1.7 MPa
at the maximum is applied to both the right and left front wheels
and the right and left rear wheels. In the meantime, it is known
that in the diagonal distribution according to the present
invention, pressure of 2 MPa or more is momently applied to the
inside front wheel and the outside rear wheel, however, the
pressure is held in a condition in which the pressure falls up to
1.6 MPa in 2.5 sec.
[0323] It is known from the slip ratio of the front and rear wheels
shown in FIG. 39 that the slip ratio of the inside front wheel in
turning (the left front wheel) rises and hereby, excessive slip
prevention control functions.
[0324] As excessive slip is prevented in a range in which a
response of a lateral motion can be secured before maximum
deceleration is acquired (at this time, the lateral force of a tire
is zero and steering does not work), this control is operated.
[0325] It is also known from time history data and a "g-g" diagram
of lateral acceleration and longitudinal acceleration respectively
shown in FIG. 40 that deceleration in the present invention
decreases. Further, FIG. 41 shows a steering angle and a response
of a yaw rate for a steering angle. There is a part in which the
gain of a yaw rate in the present invention decreases, compared
with that in G-Vectoring lateral equal distribution. In such a
situation, as a degree of the increase of a yaw rate grows dull
even if a steering angle is increased, a driver steers too much and
can easily enter a nonlinear area. For such a reason, in this
control, the diagonal distribution is required to be switched to
the lateral equal distribution based upon lateral acceleration,
longitudinal acceleration or the product of lateral acceleration
and longitudinal acceleration.
[0326] Postscript 1) When the excessive slip prevention control is
turned off, the inside front wheel is locked and deviates outside
the course.
[0327] Postscript 2) The inside front wheel deviates from the
course completely without G-Vectoring and control and afterward, is
spun (as no deceleration is made, the speed does not decrease and
lateral acceleration becomes approximately 1 G).
[0328] FIG. 42 shows the whole configuration of a third embodiment
of the vehicular motion control system according to the present
invention.
[0329] Differently from the second embodiment, a vehicle 2011 in
the third embodiment is a front engine rear drive (FR) vehicle in
which a left rear tire 2063 and a right rear tire 2064 are driven
by a front engine (2002) via a propeller shaft 2003 and a
differential gear 2100. Besides, rear wheels are suspended by
so-called multi-link suspensions 2200, 2210. The other
configuration is the similar to that in the second embodiment.
[0330] FIG. 43 shows a situation in which compliance steer is
generated when deceleration is applied to the rear wheel (the right
rear wheel in FIG. 43) in the third embodiment. A knuckle of the
rear wheel is supported by a radius link 2211 supported by a bush
displaceable in a toe moving direction, a front lower link 2212 and
a rear lower link 2213 respectively different in length (the upside
of a paper surface in FIG. 43 is equivalent to a direction of the
front of the vehicle. That is, FIG. 43 is a top view showing the
right rear wheel). In this situation, when longitudinal force
(deceleration) is applied to a wheel center, the right rear wheel
is stretched backward in the vehicle. At this time, as the front
lower link 2212 and the rear lower link 2213 are different in
length and their support points are different, variation in
alignment occurs in a direction of toe-in when the right rear wheel
is displaced backward. This direction is an entirely reverse
direction to a torsion beam type rear suspension often used in an
FF vehicle in which deceleration is basically applied in a
direction of toe-out and control timing different from control
timing in the first and second embodiments is required to be
adopted. After dynamical relation between the braking and the
driving of the rear wheel in the vehicle provided with the
differential gear characteristic in this embodiment is described,
this point will be described as a best mode including its effect
below.
[0331] FIG. 44 shows the configuration of a power train (the engine
2002, the propeller shaft 2003 and the differential gear 2100) for
the rear wheels and left and right brakes 2073, 2074 for the rear
wheels in the third embodiment of the present invention. The
differential gear has so-called open differential structure in
which no differential limiting mechanism is provided. First, the
configuration of the differential gear 2100 will be described. A
drive pinion 2101 is fixed to an end of the propeller shaft 2003
driven by the engine 2002 and drives a ring gear (a drive gear)
2102. A differential case is fixed to the ring gear 2102 and a
pinion mated shaft bearing 2103 that supports a pinion mated shaft
2104 is fixed to the differential case. Pinion mated gears 2105,
2106 are engaged with a right rear wheel side gear 2107 and a left
rear wheel side gear 2108. A right rear wheel drive shaft 2109
pierces (rotatably supports) the ring gear 2102 and connects with
the right rear wheel 2064 (however, a constant-velocity universal
joint and others are omitted). Besides, a disc rotor is attached to
the right rear wheel drive shaft 2109 and braking torque can be
applied by a brake caliper 2074 of the right rear wheel. Similarly,
a left rear wheel drive shaft 2110 connects with the left rear
wheel 2063. Besides, a disc rotor is attached to the left rear
wheel drive shaft 2110 and braking torque can be applied by a brake
caliper 2073 of the left rear wheel.
[0332] When the revolution speed of the propeller shaft 2003 is
.omega..sub.PTE, the revolution speed .omega..sub.RG of the ring
gear 2102 has a value acquired by dividing .omega..sub.PTE by final
speed reducing ratio. The engine speed of the engine 2002 and the
revolution speed of the drive shaft 2003 are omitted, the
revolution speed .omega..sub.RG of the ring gear 2102 is adopted as
representative revolution speed of the power train including the
engine, relation between the revolution speed .omega..sub.WL of the
left drive shaft 2110 and the revolution speed .omega..sub.WR of
the right drive shaft 2109 will be described below, and dynamical
relation related to the present invention will be disclosed
below.
[0333] An equation of a rotary motion related to the ring gear 2102
is shown as a mathematical expression 22 below.
I.sub.BEPT{dot over
(.omega.)}.sub.RG=k.sub.FT.sub.E-(T.sub.ER+T.sub.EL) (Mathematical
expression 22)
[0334] In this case, I.sub.BEPT is acquired by converting the
moment of inertia of the power train including the engine and the
vehicle body equivalent moment of inertia in terms of the ring gear
and is by far greater, compared with the total moment of inertia of
rotating mechanisms around axles described later. Besides, k.sub.F
is total speed reducing ratio from the engine 2002 to the ring
gear, T.sub.E is engine torque, T.sub.ER is reaction torque applied
from the right rear wheel, and T.sub.EL is reaction torque applied
from the left rear wheel.
[0335] Besides, an equation of a rotary motion of the left rear
wheel is as follows.
I.sub.WL{dot over
(.omega.)}.sub.WL=T.sub.EL-F.sub.WXLR.sub.WL-T.sub.BL (Mathematical
expression 23)
I.sub.WL is the total moment of inertia of rotary parts including
the left rear wheel, a brake disc and the drive shaft. In addition,
T.sub.EL is driving torque by the engine. Further, F.sub.WXL is
longitudinal force generated in the left rear wheel tire, R.sub.WL
is a radius of the left rear wheel tire, and T.sub.BL is braking
torque by the brake caliper 2073 of the left rear wheel.
[0336] Besides, an equation of a rotary motion of the right rear
wheel is as follows.
I.sub.WR{dot over
(.omega.)}.sub.WR=T.sub.ER-F.sub.WXRR.sub.WR-T.sub.BR (Mathematical
expression 24)
I.sub.WR is the total moment of inertia of rotary parts including
the right rear wheel, a brake disc and the drive shaft. In
addition, T.sub.ER is driving torque by the engine. Further,
F.sub.WXL is longitudinal force generated in the right rear wheel
tire, R.sub.WR is a radius of the right rear wheel tire, and
T.sub.BL is braking torque by the brake caliper 2074 of the right
rear wheel.
[0337] Further, the following rotation constraint expression
ordinarily comes into effect because of a characteristic of the
differential gear 2100 as a differential gear train.
.omega..sub.RG=1/2(.omega..sub.WL+.omega..sub.WR) (Mathematical
expression 25)
[0338] That is, the above-mentioned relation is relation that the
revolution speed of the ring gear 2102 is necessarily a mean value
of the revolution speed of the right and left wheels. The basic
expressions of the rotary parts of the vehicle provided with the
differential gear have been described.
[0339] Next, FIG. 45 is an explanatory drawing related to
longitudinal velocity vectors in positions of the right and left
rear wheels of the vehicle 2011 according to the present invention
that turns leftward. The vehicle advances at velocity V at a slip
angle .beta. in a longitudinal direction of the vehicle and a yaw
rate around the center of gravity of the vehicle at that time is r.
The speed in the longitudinal direction in the center of gravity of
the vehicle at this time is u (=Vcos.beta.). Longitudinal velocity
in the position of the right rear wheel at this time is as
follows.
u out = u + 1 2 d r ( Mathematical expression 26 ) ##EQU00009##
Only a yaw rate component accelerates, compared with longitudinal
speed in the center of gravity. However, d denotes distance (a
tread) between the right and left rear wheels. Besides,
longitudinal velocity in the position of the left rear wheel is as
follows.
u.sub.in=u-1/2dr (Mathematical expression 27)
Only a yaw rate component decelerates, compared with that in the
center of gravity of the vehicle.
[0340] First, a case that no braking force/driving force is applied
to the right and left rear wheels in the vehicle 2011 will be
described referring to FIG. 46. The velocity .omega..sub.in0 and
.omega..sub.out0 of the left and right rear wheels 2063, 2064 which
are also the inside and outside rear wheels are expressed as
follows.
.omega. Win 0 = u in R Win , .omega. Wout 0 = u out R Wout (
Mathematical expression 28 ) ##EQU00010##
When the mathematical expression 28 is considered together with the
mathematical expressions 26, 27, it is known that the revolution
speed of the inside wheel (the left rear wheel 2063) is slower than
the revolution speed of the outside wheel (the right rear wheel
2064).
[0341] The slip ratio of the inside and outside rear wheels at this
time is as follows.
S inB = u in - R Win .omega. Win u in = 0 , S wouB = u out - R Wout
.omega. Wwou u out = 0 ( Mathematical expression 29 )
##EQU00011##
The respective slip ratio is zero. That is, the expression shows
that no force is generated in the longitudinal direction.
[0342] Further, as the mathematical expression 22 comes into
effect, as follows.
.omega. RG 0 = 1 2 ( .omega. Win 0 + .omega. Wout 0 ) = u R w (
Mathematical expression 30 ) ##EQU00012##
That is, the expression shows that the revolution speed of the ring
gear 2102 is determined by longitudinal velocity in the center of
gravity of the vehicle independent of the yaw rate and a tread of
the vehicle.
[0343] A case that in such a condition of leftward turning, braking
torque T.sub.BR is applied to the right rear wheel which is the
outside rear wheel in turning from the brake caliper 2074 of the
right rear wheel as shown in FIG. 47 will be described below.
First, an effect on the ring gear 2102 and the rotary parts when
braking torque T.sub.BR is applied will be described.
[0344] First, when T.sub.EL and T.sub.ER are deleted using the
mathematical expressions 22, 23, 24, as follows.
.omega. . RG = 1 I BEPT { I W ( .omega. . L + .omega. . R ) + R W (
F WXL + F WXR ) + ( T BL + T BR ) } ( Mathematical expression 31 )
##EQU00013##
Besides, when the mathematical expression 25 is differentiated by
time, as follows.
.omega. . RG = 1 2 ( .omega. . WL + .omega. . WR ) ( Mathematical
expression 32 ) ##EQU00014##
When this mathematical expression is assigned to the mathematical
expression 31 and it is coordinated, as follows.
.omega. . RG = - R W ( F WXL + F WXR ) + ( T BL + T BR ) I BEPT + 2
I W ( Mathematical expression 33 ) ##EQU00015##
However, for the effective radius of the tire and the moment of
inertia of the tire, those of the right and rear wheels are set to
the same.
[0345] When the mathematical expression 33 is partially
differentiated by T.sub.BR so as to search into the variation of
the velocity of the ring gear 2102 when braking torque T.sub.BR is
applied from the brake caliper 2074 of the right rear wheel, the
following mathematical expression is acquired.
.differential. .omega. . RG .differential. T BR = - 1 I BEPT + 2 I
W ( Mathematical expression 34 ) ##EQU00016##
In the meantime, when the velocity variation gain of the right rear
wheel 2064 is considered when braking torque T.sub.BR is applied
from the brake caliper 2074 of the right rear wheel, the following
expression is acquired.
.differential. .omega. . WR .differential. T BR = - 1 I W (
Mathematical expression 35 ) ##EQU00017##
As described above, I.sub.BEPT is extremely great, compared with
I.sub.W. The mathematical expressions 34, 35 tell that even if
braking torque T.sub.BR is applied from the brake caliper 2074 of
the right rear wheel, the gain of velocity variation given by the
variation of the velocity of the ring gear 2102 is low and the
revolution speed of the ring gear 2102 hardly varies by small
braking torque. Even if braking torque T.sub.BR acts on the right
rear wheel in leftward turning which is currently supposed, the
velocity of the ring gear is fixed to u/R.sub.W as shown in FIG. 47
and it is considered that the velocity of the rear gear hardly
varies. That is, as follows.
.omega. . RG 0 = 1 2 ( .omega. . Win 0 + .omega. . Wout 0 )
.apprxeq. 0. ( Mathematical expression 36 ) ##EQU00018##
Besides, as follows.
{dot over (.omega.)}.sub.Win.apprxeq.-{dot over (.omega.)}.sub.Wout
(Mathematical expression 37)
As a result, the fall of the revolution speed of the outside tire
has an effect upon the increase of the revolution speed of the
inside tire. When braking torque is applied to the right (outside)
rear wheel in leftward turning, the velocity
.omega..sub.out.sub.--.sub.oB of the right (outside) rear wheel may
be smaller than the velocity .omega..sub.Wout0 of the outside rear
wheel in turning before the braking torque is applied and the
velocity .omega..sub.in.sub.--.sub.oB of the left (inside) rear
wheel may be greater than the velocity .omega..sub.Win0 of the
outside rear wheel in turning before the braking torque is
applied.
[0346] FIG. 48(a) shows a case of no braking when the vehicle
approaches a curve having a radius of 40 m at initial speed of
approximately 53 km/h on a pressed snowy road, FIG. 48 (b) shows a
case of braking when the same brake oil pressure (as normal) is
applied to all the wheels on the same condition, and FIG. 48C shows
the wheel speed (converted to peripheral velocity) of the outside
rear wheel and the inside rear wheel when braking is applied to
only the inside (left) front wheel in turning and the outside
(right) rear wheel in turning according to the present invention on
the same condition. As in the case shown in FIG. 48 (a), no
deceleration is made, a condition shown in FIG. 48(a) is the same
as the condition shown in FIG. 46.
[0347] FIG. 45 shows that longitudinal velocity in a position of
the inside wheel during turning is smaller than that in a position
of the outside wheel, however, FIG. 48(a) shows that when the
vehicle is turned on the radius of 40 m at 50 km/h, the inside
wheel is rotated at velocity lower than the outside wheel by
approximately 3 km/h. In the meantime, in the braking of the
outside rear wheel shown in FIG. 48(c), difference between the
outside wheel and the inside wheel is clearly reduced, compared
with other cases.
[0348] This shows that in the inside rear wheel, peripheral
velocity is faster than longitudinal velocity in its position. That
is, it can be considered that the inside rear wheel has slip ratio
in a direction of driving shown in the following mathematical
expression 38.
S in_oB = ( u - d 2 r ) - R in .omega. in_oB R in .omega. in_oB (
Mathematical expression 38 ) ##EQU00019##
[0349] Further, the effective radius of the inside tire is
relatively larger than that of the outside tire in which its load
is transferred by lateral acceleration and which is indented and
there is effect that slip ratio in the direction of driving grows
more.
[0350] FIG. 49 shows a situation in which longitudinal force of the
rear wheel is generated at this time. Braking force
F.sub.xB.sub.--.sub.r is generated in the outside rear wheel by
braking torque T.sub.BR from the brake caliper 2074 of the right
rear wheel and driving force F.sub.X.sub.--.sub.dif is generated in
the inside rear wheel though the driving force is minute. As a
result, the moment Mz for return for stopping turning shown in the
following mathematical expression 39 is generated.
M dif = d 2 ( F xBr + F xD_dif ) ( Mathematical expression 39 )
##EQU00020##
[0351] Actually, it is verified by plural observers that when a
test vehicle in which braking torque is distributed as described
above is prepared and is tested on a pressed snowy road, the moment
for return of the vehicle grows and the sense of stability clearly
increases. It is considered that an effect of the moment for return
is more sensed in a situation in which a coefficient of friction is
small as on the pressed snowy road, therefore, lateral acceleration
is small and the transfer of a load is also small.
[0352] Besides, the mathematical expression 36 (only the small
variation of the revolution speed of the ring gear is acquired by
braking torque in only the outside wheel in turning) is supposed
because of the dimension of rotational inertia force in the current
engine and the current power train, however, virtual rotational
inertia force is given and the similar effect can be also acquired
by controlling the revolution speed or the torque of the ring gear
based upon a numerical value of the engine, the power train or the
electric motor, the generator and others.
[0353] A best mode in the vehicle in the third embodiment of the
present invention which is provided with the multi-link suspension
and the differential gear and which realizes rear-wheel compliance
steer having a longitudinal force toe-in characteristic will be
disclosed below. As shown in FIGS. 50A to 50D, a control method
according to the present invention especially related to control
from the latter term of turning to steady turning will be described
again in comparison with a four-wheel active steer vehicle
referring to the nonpatent literature 5 below.
[0354] At the beginning of turning, the yaw moment applied to the
vehicle is required to be increased to enhance the turning
performance of the vehicle. For that, it is effective to increase a
steering angle of the front wheel and to increase the cornering
force of the front wheel (see (a) in FIG. 50). In the meantime, in
the third embodiment of the present invention, braking force
F.sub.xB.sub.--.sub.f is applied to only the inside front wheel in
turning as shown in FIG. 50 (b) (in the first and second
embodiments, braking force is also simultaneously applied to the
rear wheel). Hereby, braking force can be applied to only a
direction in which a steering angle is increased.
[0355] In the transient latter term till steady turning, overshoot
of the same phase is momently caused in the four-wheel active steer
shown in FIG. 50 (c). This enhances the convergence of a yaw motion
and the skid of a vehicle body is inhibited. As a result, in the
third embodiment of the present invention, braking force
F.sub.xB.sub.--.sub.r is applied to only the outside rear wheel as
shown in FIG. 50 (d). Hereby, compliance steer
.delta..sub.XB.sub.--.sub.r on the toe-in side is generated and
overshoot on the side of the same phase can be generated as in the
four-wheel active steer shown in FIG. 50 (c).
[0356] Further, minute driving force F.sub.x.sub.--.sub.dif can be
applied to the inside rear wheel (the left rear wheel), the yaw
moment for return can be directly applied, the convergence of a yaw
motion is enhanced, and the skid of the vehicle body can be
inhibited.
[0357] FIG. 51 shows a case in which G-Vectoring (proportion to a
lateral jerk) is applied to an acceleration/deceleration command
based upon a concept shown in FIG. 50 as in the first and second
embodiments. Braking force is applied mainly to the inside front
wheel at the entrance (points 1, 2) of a corner according to a
G-Vectoring control command. Besides, in the transient latter term
(at points 2, 3) till steady turning, braking force is applied
mainly to the outside rear wheel according to the G-Vectoring
control command. In escape from the corner (in the vicinity of
points 5, 6), equal driving force is applied to the right and left
rear wheels by the differential action of the rear wheels according
to the G-Vectoring control command.
[0358] FIG. 52 shows modes of control in each time. From a line in
(a) of FIG. 52, turning is started (turning performance is
enhanced) in (b) of FIG. 52, the convergence of a yaw motion is
enhanced and the skid of the vehicle body is inhibited in (c) of
FIG. 52, the turning transfers to steady turning in (d) of FIG. 52,
acceleration is made by the rear wheel in escape in (e) of FIG. 52,
and the turning is returned to a linear motion in (f) of FIG. 52.
As described above, high-quality turning can be serially provided.
It is verified by plural observers that especially, a sense of
security in a situation in which a coefficient of friction is small
as on a pressed snowy road can be greatly enhanced by adding a
condition shown in FIG. 52C.
[0359] The method of controlling braking force and driving force
applied to each wheel in a situation in which the vehicle moves on
a plane according to a longitudinal acceleration command has been
disclosed. Finally, on the supposition of a situation in which the
vehicle runs in a mountainous area, contents devised to settle a
practical problem of control so as to acquire the similar effects
of the control to a situation in which the vehicle moves on the
plane in a situation in which this system is more practically used
will be disclosed.
[0360] In a situation shown in FIG. 53, when the weight of the
vehicle for considering the variation of vehicular longitudinal
acceleration by a gravity component on a slope is M, the
gravitational component of Mgsin .theta. is applied to the vehicle
in a longitudinal direction while the vehicle descends on the slope
of an inclination .theta. as shown in FIG. 54.
[0361] When open-loop brake fluid pressure control or motor torque
control and others is made according to an
acceleration/deceleration command Gxc, the longitudinal force Fxff
of the front wheel and the longitudinal force Fxrr of the rear
wheel are controlled, actual vehicular deceleration is Gx
(=Gxc-Mgsin .theta.) differently from a deceleration command value
and the implement of target control becomes impossible.
[0362] In the meantime, real longitudinal acceleration Gx is
measured in a longitudinal acceleration sensor 22 in a combined
sensor as shown in FIG. 55, a longitudinal jerk is calculated by
multiplying the rear longitudinal acceleration by gain K1 or by
differentiating it, a value acquired by multiplying by gain K2 and
a target acceleration/deceleration command Gxt are compared, and
braking force and driving force Fxff, Fxrr have only to be
determined based upon its deviation .DELTA.Gx. The real
longitudinal acceleration can be made to follow target longitudinal
acceleration by configuring such a feedback loop independent of
disturbance such as a slope and the deterioration of control can be
reduced.
[0363] Besides, for another method, inclination information can be
also acquired using map information by GPS and NAVI. When
inclination information (grade information) can be acquired using
GPS, NAVI and further, a road grade sensing means such as an
external field sensor as described above, correction is made so
that a value in an acceleration command is larger than a value in
an acceleration command in running on a flat road surface when a
grade of a road surface is ascent and is smaller than the value in
the acceleration command in running on the flat road surface when
the grade is descent, and correction can be also made so that a
value in a deceleration command is smaller than the value in the
acceleration command in running on the flat road surface when the
grade is ascent and is larger than the value in the acceleration
command in running on the flat road surface when the grade is
descent.
[0364] Hereby, even if the vehicle runs on an inclined road
surface, a motion according to a target acceleration/deceleration
command can be realized and the similar control effects to a
situation in which the vehicle moves on a plane are acquired.
[0365] The steering angle control from the four-wheel active steer
control, the compliance steer by braking force and driving force
and the acceleration/deceleration control (the G-Vectoring control)
linked with a lateral motion have been described, the basic concept
of the present invention in which these are organically combined
has been described, and the effectiveness of the present invention
has been described using the two embodiments, the result of
computer simulation and the result of vehicle tests. According to
the present invention, the compliance steer can be actively
controlled using braking force/driving force, and the technique and
the system that enable enhancing the operability and the stability
with sufficient effects with the light system can be provided.
LIST OF REFERENCE SIGNS
[0366] 0, 2010 Vehicle [0367] 1 Left rear-wheel motor [0368] 2
Right rear-wheel motor [0369] 7 Power steering [0370] 10
Accelerator pedal [0371] 11 Brake pedal [0372] 16 Steering wheel
[0373] 21 Lateral acceleration sensor [0374] 22 Longitudinal
acceleration sensor [0375] 23, 24, 25 Differentiating circuit
[0376] 31 Accelerator position sensor [0377] 32 Brake pedal
position sensor [0378] 33 Driver steered angle sensor [0379] 38 Yaw
rate sensor [0380] 40 Central controller [0381] 44 Steering
controller [0382] 46 Power train controller [0383] 48 Pedal
controller [0384] 51 Accelerator reaction motor [0385] 52 Brake
pedal reaction motor [0386] 53 Steer reaction motor [0387] 61,
1011, 2061 Left front wheel [0388] 62, 1012, 2062 Right front wheel
[0389] 63, 1013, 2063 Left rear wheel [0390] 64, 1014, 2064 Right
rear wheel [0391] 70 Millimeter wave ground vehicle speed sensor
[0392] 121 Left front-wheel motor [0393] 122 Right front-wheel
motor [0394] 200 Combined sensor [0395] 401 Vehicular motion model
[0396] 402 G-Vectoring controller [0397] 403 Yaw moment controller
[0398] 404 Braking force/driving force distributor [0399] 410
Signal processing unit [0400] 451, 452 Brake controller [0401]
1003, 1103, 1123, 1124, 1004, 1104 Knuckle arm [0402] 1005, 1105,
1125 Tie rod [0403] 1006, 1106, 1126 Gear box [0404] 2002 FR
vehicle [0405] 2003 Propeller shaft [0406] 2063, 2064 Rear tire
[0407] 2100 Differential gear [0408] 2101 Drive pinion [0409] 2102
Ring gear [0410] 2103 Pinion mated shaft bearing [0411] 2104 Pinion
mated shaft [0412] 2105, 2106 Pinion mated gear [0413] 2107, 2108
Side gear [0414] 2109, 2110 Drive shaft [0415] 2200, 2210
Multi-link suspension [0416] 2211 Radius link [0417] 2212 Front
lower link [0418] 2213 Rear lower link
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